Holy Scripture distinguishes several classes of Angels. Theologians divide the Angels into three hierarchies, each of which contains three orders, or Choirs:
Angels, Archangels, Virtues;
Powers, Principalities, Dominations;
Thrones, Cherubim, Seraphim.

Traditionally the Nine Choirs are listed in ascendant order, although the Chaplet of St. Michael, in which all nine Choirs are honored and invoked, lists them in descendant order. This does not matter as along as we understand that there exists a hierarchy of Angels with special attributes and functions assigned to each.

Only three Angels are mentioned in Scripture by name: Michael-----"Who is like God?", Gabriel-----"Man of God," and Raphael------"God heals."
 

The Angels of the  First Choir
Angels

Though all the blessed Spirits are commonly called Angels, it is to those of the First Choir that the appellation strictly applies. They are charged with the execution of the Divine ordinances, and are appointed the Guardians of men. Humility is the virtue particularly ascribed to them-----for though the least among the Choirs, yet they see their celestial companions without desiring their greater, more excellent endowments.

The Guardian Angels

They exercise continual watchfulness over the souls committed to their care. Their number is exceedingly great, and it is not necessary when an Angel has accompanied his charge into Heaven, that he be again assigned to a soul in any future generation. Our Guardian, who is our companion in life, will also be forever at our side in Heaven. The joy of these Angels is immeasurably increased when souls entrusted to their care enter Heaven. The Guardian Angels of the lost souls are not deprived of their share of joy. God in His justice increases also theirs with the others, and then assigns them to the special guard of the Queen of Angels, where they with great joy praise the Infinite Justice of God.

Guardian Angels differ from one another. Some appear more active and energetic than others. Some are more reserved, I might almost say, more timid, and these are assigned to persons who are called to suffer much. They appear dressed in red and wear a small crown. Other Guardian Angels are dressed in white, their expression is always joyful, a beautiful crown adorns the head, they are the Angels assigned to innocent souls, and they are servants of such souls rather than companions.

Children have exceedingly lovely Angels. Their garments are light blue, decorated with pearls, and a wreath of beautiful everlasting roses surrounds the head, their hands are always folded in prayer and their eyes continually directed towards Heaven.

The Angels of sinners have a beautiful majestic bearing. Their garments are of a deep red color, a crown adorns the head, their arms folded across the breast, and their faces turned upwards to Heaven with an imploring and painful expression. How deeply must a mortal sin offend God when His Angels are filled with such grief. Holy souls who live in very unChristian surroundings and persons who have a special mission to perform, receive special Angels from God.

There is nothing more lovely than a Guardian Angel, nothing more gracious than the goodness of God, Who loves our souls so much that He assigns Angels to watch over them, to guide and even to serve them. My most faithful friend, my dearest brother, my holy Angel, I greet thee a thousand times in the name of Jesus and I thank God that He made thee so beautiful and so powerful.

Guardian Angels are Helped by Angels of the Higher Orders

When a person is firmly on the road to perfection, he receives in addition to his Guardian Angel, other Angels of the higher orders, of the third and fourth choirs, the Virtues and Powers. [Magdalen writes to one of her spiritual children, a religious, "Your second Angel is from the company of St. Gabriel, therefore a brother of my beloved Archangel. I often see my Angel, I send him to help my spiritual children, and I ask him often for his help. He appears as a tall beautiful Angel with golden brown hair; he is reserved and recollected as in God's presence, but at times he smiles so Heavenly, particularly when I remind him of the needs of my spiritual children. All those who belong to the Confraternity of Blessed Grignon de Montfort of Mary, Queen of Hearts, have two Angels, the ordinary Angel and an Archangel taken from the company of St. Gabriel.

Let us, like the humble Guardian Angels, love the lowest place, especially when placed therein by Divine Providence, and to behold with joy the preference given to others.

Practice-----Three Acts of Humility, interior and exterior.

Aspiration----- "Who is like God."

The Angels of the Second Choir
Archangels

The Archangels are distinguished from the Angels by the greater importance of their functions: the Guardians of those invested with authority in the Church and State-----and are remarkable for their love and care of men. Let us imitate them, doing our neighbor all the good we can and invoking in his behalf these Blessed Spirits.

The Archangels

Veneration of the Archangels brings such strength and consolation. The Archangels are divided into different groups and appear dressed in different colored garments. Members of this choir are the seven holy spirits who stand before the throne of God, ever ready to announce His commands.

St. Michael

St. Michael stands next to God the Father. He is clothed like a warrior, and his beauty is most majestic. The Angels of his company also appear as warriors. These Archangels are sent to strengthen Martyrs in their torments and to support those who must suffer persecution for God's sake. In such hours of trial God in His great goodness bids St. Michael to send Angels of his company to assist the Guardian Angels in strengthening such souls in their great need. With this help these happy souls are then able to perform the most heroic acts of self-denial and show the most unflinching courage in their sufferings. How seldom, though, do they remember that they owe all this to their Angels and how little thanks do they give them. The AngeIs are so constant and faithful in their service of men, and men are so fickle and forgetful in their duties toward the Angels.

St. Gabriel

St. Gabriel wears priestly vestments, an alb and a stole. He is the special messenger of The Holy Spirit. His gifts place him next to St. Michael. He has charge of the children of the Holy Spirit, of priests, and of all souls who practice a special devotion to the Holy Spirit or at least wish to honor Him in a particular way. St. Gabriel is the patron of contemplative prayer. Priests should allow no day to pass without invoking his help, particularly before preaching the word of God. Those too, who must suffer great spiritual and physical pains, should call on him for strength. St. GabrieI is able to obtain for us a deep and sincere devotion to the Mother of God. SouIs who greet him often in lifetime will be greeted by him in their dying moments, and he will bear their souls to his Heavenly Queen. St. Gabriel's beauty is of a more lovely, impressive, and touching character, not so overpowering as the majesty of  St. Michael.

I was once kneeling before the crucifix and meditating on the patience of Our Blessed Mother in her great sufferings. As I wept bitter tears in sympathy with the Virgin Mother, I suddenly noticed a beautiful odor in the room. The room also became bright and St. Gabriel appeared, who said to me with great joy, "Blessed are you and your holy tears." I closed my eyes un able to bear the shining brightness of the Angel of the Lord. As I opened them, I also beheld the Mother of God, so beautiful and amiable. St. Gabriel turned to me and said, "you suffer with Mary, you should also rejoice with her. You have never prayed the rosary of her seven joys, but do so often. This rosary brings much joy to all who pray it and also great joy to our Heavenly Queen. Tell your spiritual children to practice this devotion. Greet them in the names of Jesus and Mary, and tell them that my Queen loves them much and is ever at their side because they spread devotion to me and to the other Angels, which causes great joy for the Queen of Angels."

The Guardian Angels of Christ

St. Gabriel brought the message to the three kings, who were Gentiles, that they should go to Bethlehem. When praying the Angelus, let us also Greet St. Gabriel. It was with the greatest pleasure that he heard the beautiful words spoken by Mary the first time, "Behold the handmaid of the Lord." He bowed with deepest reverence when the Word was made Flesh. St. Gabriel was the Guardian Angel of the human nature of Christ. He was the first to announce the birth of Christ to the shepherds, he accompanied the Holy Family on the flight into Egypt, he was the Angel who came to Christ when He sweat blood in the garden of Olives, he stood by the Mother of God at the meeting with her Son, and he assisted Our Lord in His dying agony on the Cross. He was also the Angel of the Resurrection and of the Ascension. Anyone who practices a special devotion to St. Gabriel, will be strengthened and comforted by him in the last hour, because St. Gabriel stood by Our Savior at His death.

The First Servants of the Virgin Queen

The Annunciation. The Immaculate Virgin possessed the most exquisite beauty and a deep humility of which she was wholly unaware. Her eyes were downcast and she did not notice the blinding brightness which emanated from herself. The Archangel who brought the message to Mary, knelt before her, and as The Holy Spirit overshadowed her, he fell on his face . . . some  Archangels are called Guardians and Protectors of Priests even though the Third [mortification], Fourth [parishes],  Fifth [priests], and Sixth Choirs [missionaries and preachers] are specifically charged with the care of those invested with ordination and the spread of the Catholic faith, as you will read below.
 

St. Raphael: Angel of Joy

"Joy be to thee always" [Tob. 5: 11], the Angel Raphael said when he greeted the elder Tobias. And as the Scriptures tell us, these words of St. Raphael were fulfilled:

"And after Tobias was restored to his sight, he lived two and forty years, and saw the children of his grandchildren. And after he had lived a hundred and two years, he was buried honorably in Niniveh. For he was six and fifty years old when he lost the sight of his eyes, and sixty when he recovered it again. And the rest of his life was in joy, and with great increase of the fear of God he departed in peace .  . .

"And it came to pass that after the death of his mother, Tobias [the younger] departed out of Niniveh with his wife, and children, and children 's children, and returned to his father-in-Iaw and mother-in-law. And he found them in health in a good old age: and he took care of them, and he closed their eyes: and all the inheritance of Raguel's house came to him: and he saw his children's children to the fifth generation. And after he had lived ninety-nine years in the fear of the Lord, with joy they buried him. And all his kindred, and all his generation continued in good life, and in holy conversation, so that they were acceptable both to God, and to men, and to all that dwelt in the land." [Tob. 14: 1-4, 14-17].

"And the rest of his life was in joy"-------what wonderful words!

Joy at all times? Yes, even when we are most sorely tried. For, apart from the usual blessings of life that make us rejoice [and which we too often take for granted], we should also be glad when God sends us a cross to remind us of His own sufferings on Calvary. How often it is that only through some pain or grief do we turn our thoughts to God! When we are self-satisfied and pleased, we tend to forget about Him.

Above all, do not grumble or become despondent if your prayers are not answered immediately, or exactly the way you want! God may have other plans for you, infinitely better than any you dreamed of. Trust Him!

Practice-----Two Acts of Charity, with great affection.

Aspiration----- "Holy Archangels! pray for us, and for our priests."

The Angels of the Third Choir
Virtues

Energy and strength are attributed to the Virtues. They have dominion over the elements; all nature is subjected to their control. Hence they can raise or appease the tempest. We may profitably invoke them in unforeseen accidents, sickness, etc. We may also have recourse to them for that strength necessary to lead a penitential life, and root out the inclinations of depraved nature.

The Angels of the Third choir, the Virtues, are clothed in blue and girded with gold. A broad golden crown encircles the head and a bright star shines above the forehead. They are as their name indicates personified power or virtue. God assigns them to such persons who strive unceasingly with all their soul to sanctify themselves, and who, even after they have successfully uprooted their failings, still continue to apply all possible remedies of spiritual and corporal penance to make certain their eternal salvation. Some priests have an Angel of this choir ever at their side. Such priests are usually very self-sacrificing, very strict with themselves, and do not tire in mortifying themselves. Such souls are the favored ones of the Virtues. Some great sinners receive such an Angel after their conversion. The Angel admonishes them night and day, and the penitents never weaken in following their guidance, for these Angels have the power necessary to help them persevere. All persons inclined to the contemplative life should call on this choir of Angels for help, for good thoughts alone do not make holy, one needs also strength to persevere and to accomplish this great task.

Practice-----Visit the Blessed Sacrament to obtain grace to overcome your evil inclinations, etc.