Notes on Biblical Angelology
I used to think all Cherubs had 4 heads, as per Ezekiel, but this position is clearly untenable.
Rather, it seems (to me) Cherub is the OT general term for “celestial humanoid,” (angel as it were,) like the NT uses the term “messenger”, (Aggelos) often without the slightest reference to them fulfilling a messenger-function (like we do today with the Anglicized form angel.)
Cherub might in fact be the closest we get to a unique term to describe that “race” of humanoid beings in the heavens.
Rather than the Cherub being a “type of angel”, it seems instead the messengers (Malakim / Aggeloi) and “Burning Ones” (Seraphim) and “Living Creatures” (Chayot) and so forth are all types of Cherubim (per the OT.)
Maybe these passages will be helpful, showing some different types of Cherubim:
four-faced/headed Cherubim (man, lion, ox, eagle)
four-faced/headed Cherubim (“cherub,” man, lion, eagle)
two-faced/headed Cherubim (man, lion)
one-faced Cherubim (each with a different apperance: lion, calf, man, eagle)
Clearly the two Cherubim “of hammered gold” on the cover of the Ark of the Covenant (made in the days of Moses) were of the one-faced variety, typically understood to be winged humanoids (with human faces.)
Solomon later made a pair of Cherubim “of olive wood, each ten cubits high” (1 Kings 6:23.)
The “sons of God” (Beney Elohim) being likely synonymous with the Beney Elyon (“sons of the Most High”) and the Sarim (“princes”) of Daniel 10:13 are all understood as similarly humanoid as well.
In chapters 1 and 10 of Ezekiel we are told of certain “wheels”, called the “Hagalgal” (Ez. 10:13), described as having the spirit of life in them; a common interpretation is that the spirit of the Cherubim is somehow mystically attached to these wheels. Like the Cherubim of the same vision, they are covered in eyes.
Discounting Satan’s appearance in Gen. 3:1, (in light of Ezekiel 28:14 and 16 where he is called a “covering Cherub”, כרוב הסכך), the very first instance of Cherubim in the Bible is Gen. 3:24, where an unspecified number are tasked with guarding the tree of life, along with “a flaming sword” (singular) which “turned every way,” giving the impression of a flying sword, rather than something being grasped by (one of) the Cherubs.
In Psalm 18:10 and 2 Samuel 22:11 God is described as riding upon the Cherubim, acting as his “living chariot” (or Merkabah, being almost but not completely an anagram for Cherubim), compare 1 Chronicles 28:18.
[This concept may have been the inspiration for Muhammed’s ride upon Al-Buraq, another word anagrammatic for Cherub.]
The term messenger is of course used to describe human messengers as well as heavenly ones.
The term Nachashim Seraphim (הנחשים השרפים) is used in the singular and in the plural (Num. 21:6, Deut. 8:15) to describe what is usually translated as “fiery serpents” which is interesting; the brazen serpent, used to heal those bitten by the fiery serpents, is initially simply called a Seraph (Num. 21:8) and then a brazen serpent (נחש נחשת, Num. 21:9).
In 2 Kings 18:14 it is called Nechushtan (נחשתן).
While there likely was something supernatural about these serpents, they were not synonymous with “Seraphim.”
Although the 70 Sarim are obviously the highest-ranking of the angels, it is otherwise impossible to establish an “angelic hierarchy” as it were; indeed, it is nigh-impossible to even separate and categorize those angels/Cherubim mentioned in the Bible, which likely does not cover each kind as it were.
And what is rank anyway ?
The many-faced ones appear to be closer to God than the Sarim, though not specified to hold any authority over anyone else. In that sense their privilege could be said to be higher, though being without authority.
The attempts at writing down angelic hierarchies have been a cause for embarassment, whether Christian or Jewish.
Not only do they presume that all the different types of heavenly creatures have been revealed to us, but they regularly ignore what the Bible has to say about it.
For example the Chayot are explicitly labelled by Ezekiel as Cherubim (Ez. 10:20) which is, as far as I can see, not reflected in any of the many studies on angelic hierarchy.
Sometimes they even make up angels, eg. אראל (Strong’s #691) and חשמל (Strong’s #2830) are interpreted as obfuscated references to angelic beings in the angelology of Maimonides and the Kabbalists.
Not to mention that they all perpetuate the unbiblical concept of multiple archangels in spite of the Bible only discussing the subject in the singular (Jude 1:9, 1 Thess. 4:16) with at least one of the instances being a reference to the Messiah. 
The 24 elders (Rev. 4:4) mentioned throughout the revelation, being the heavenly counterpart to the 24 orders of the Levitical priesthood, are routinely ignored as well.
On the other hand, thrones, principalities, rulers and dominions are frequently set into categorization, though these may well be overlapping and generic terms. 
Sometimes they are conflated with the Sarim and/or “archangels (plural).”
~~ Abel Zechariah, 5 Dec. 2012
 Confer John 5:25, describing the same event as 1 Thess., namely the event of the Messiah calling up the dead to life by a mighty shout.
One also wonders how, by definition, there can be more than one “chief messenger,” as is the meaning of the word.
 Many Bibles, inclding the KJV, are also inconsistent about the translations of these terms:
in its rendition of Col. 1:6, thrones is thronoi, principalities is archai, dominions is kyriotetes, and powers is exousiai; whereas in 1 Cor 15:24 archen is rule, exousian is authority, and dynamin is power.