This has already been discussed to death, but it would be too long to find the previous threads without a working search function.
I'd just like to recall that besides the apocalyptic tradition (to which 1 Thessalonians, Jude and Revelation belong in their own ways) which generally numbers several archangels, including Michael, there is another, Hellenistic use of the term archangel which is attested in Philo. There archangel is an alternate title for the one Logos or "Son of God" which is also described as the firstborn and eldest of angels (which are, according to the allegorical trend, described in a much less "personal" way than in the apocalyptic tradition).
De Confusione linguarum 146: "And even if there be not as yet any one who is worthy to be called a son of God, nevertheless let him labour earnestly to be adorned according to his first-born word, the eldest of his angels, as the great archangel of many names; for he is called, the authority, and the name of God, and the Word, and man according to God's image, and he who sees -- Israel.
Ibid., 63 "For the Father of the universe has caused him to spring up as the eldest son, whom, in another passage, he calls the firstborn (prôtogonos). And he who is thus born, imitating the ways of his father, as formed such and such species, looking to his archetypal patterns."
Interestingly, while
christological NT texts (Johannine, Pauline and post-Pauline) draw on this set of Hellenistic concepts they consistently avoid any
angelic reference to Jesus Christ (and Hebrews which is perhaps the most Hellenistic work of all dismisses the notion explicitly -- the Son is
not an angel). I guess the main reason is that they were inclined to take the apocalyptic angelology much more
realistically than Philo did (angels are seen as real, personal, distinct creatures in heaven, not allegorical figures). In this perspective, it is pretty clear that the NT references to Michael and/or "archangel" do not apply to Jesus. However, there was probably an angelic christology too in early Christianity: the Hellenistic talk attributed to Stephen in Acts 7 might suggest it (note v. 15, 30, 35, 38), and it clearly surfaces in some Church Fathers, especially Justin Martyr -- here are a few examples from the
First Apology:
6:
Hence are we called atheists. And we confess that we are atheists, so far as gods of this sort are concerned, but not with respect to the most true God, the Father of righteousness and temperance and the other virtues, who is free from all impurity. But both Him, and the Son (who came forth from Him and taught us these things, and the host of the other good angels who follow and are made like to Him), and the prophetic Spirit, we worship and adore, knowing them in reason and truth, and declaring without grudging to every one who wishes to learn, as we have been taught.
22:
Moreover, the Son of God called Jesus, even if only a man by ordinary generation, yet, on account of His wisdom, is worthy to be called the Son of God; for all writers call God the Father of men and gods. And if we assert that the Word of God was born of God in a peculiar manner, different from ordinary generation, let this, as said above, be no extraordinary thing to you, who say that Mercury is the angelic word of God.
53:
And all the Jews even now teach that the nameless God (another Philonian notion) spake to Moses; whence the Spirit of prophecy, accusing them by Isaiah the prophet mentioned above, said "The ox knoweth his owner, and the ass his master's crib; but israel doth not know Me, and My people do not understand." And Jesus the Christ, because the Jews knew not what the Father was, and what the Son, in like manner accused them; and Himself said, "No one knoweth the Father, but the Son; nor the Son, but the Father, and they to whom the Son revealeth Him." Now the Word of God is His Son, as we have before said. And He is called Angel and Apostle; for He declares whatever we ought to know, and is sent forth to declare whatever is revealed; as our Lord Himself says, "He that heareth Me, heareth Him that sent Me." From the writings of Moses also this will be manifest; for thus it is written in them, "And the Angel of God spake to Moses, in a flame of fire out of the bush, and said, I am that I am, the God of Abraham, the God of Isaac, the God of Jacob, the God of thy fathers; go down into Egypt, and bring forth My people." And if you wish to learn what follows, you can do so from the same writings; for it is impossible to relate the whole here. But so much is written for the sake of proving that Jesus the Christ is the Son of God and His Apostle, being of old the Word, and appearing sometimes in the form of fire, and sometimes in the likeness of angels; but now, by the will of God, having become man for the human race, He endured all the sufferings which the devils instigated the senseless Jews to inflict upon Him; who, though they have it expressly affirmed in the writings of Moses, "And the angel of God spake to Moses in a flame of fire in a bush, and said, I am that I am, the God of Abraham, and the God of Isaac, and the God of Jacob," yet maintain that He who said this was the Father and Creator of the universe. Whence also the Spirit of prophecy rebukes them, and says, "Israel doth not know Me, my people have not understood Me." And again, Jesus, as we have already shown, while He was with them, said, "No one knoweth the Father, but the Son; nor the Son but the Father, and those to whom the Son will reveal Him." The Jews, accordingly, being throughout of opinion that it was the Father of the universe who spake to Moses, though He who spake to him was indeed the Son of God, who is called both Angel and Apostle, are justly charged, both by the Spirit of prophecy and by Christ Himself, with knowing neither the Father nor the Son. For they who affirm that the Son is the Father, are proved neither to have become acquainted with the Father, nor to know that the Father of the universe has a Son; who also, being the first-begotten Word of God, is even God. And of old He appeared in the shape of fire and in the likeness of an angel to Moses and to the other prophets; but now in the times of your reign, having, as we before said, become Man by a virgin, according to the counsel of the Father, for the salvation of those who believe on Him, He endured both to be set at nought and to suffer, that by dying and rising again He might conquer death. And that which was said out of the bush to Moses, "I am that I am, the God of Abraham, and the God of Isaac, and the God of Jacob, and the God of your fathers," this signified that they, even though dead, are let in existence, and are men belonging to Christ Himself. For they were the first of all men to busy themselves in the search after God; Abraham being the father of Isaac, and Isaac of Jacob, as Moses wrote.
There is a pretty clear theological line running from Philo to Justin via "Stephen". Why it did not make its way into a NT "angelic christology" -- which eventually included the opposite stance in Hebrews -- is, I think, the result of the settling of both dogma and canon by the 4th century.
Last edit to add that an "angelic christology" does not mean a "low christology" (à la WT). In the Dialogue with Trypho Justin goes to great lengths to defend his angelic christology, yet repeatedly insists that the Son is "both Angel and God".
