The Choirs are a theological construct, so they arent set in stone, and most of the theological ideology comes from the Apokrapha sinse there is only a passing mention of Angels here and there in Scripture. The Highest order of Angels do nothing but Worship. They generally are permanent residents in Heaven. These are the Host who probably do the stuff you read about in Revelation, or they become GODs entourage when in the Old Testament he actually appears. Seraphs and Cherubs...Possibly the most famous Seraphim is Lucifer, and the most famous Cherub is the Guard who was put at the entrance to Eden to gaurd the Tree of Life after the Fall.
Thrones are Angels that GOD uses in creation, the likely hood is that there are many thrones, its likely that each Pregnant woman for example has come into contact with a Throne, without knowing it. These are the least likely type to ever take on a form because they are more of a creative substance then an actual humanoid-creature with wings. Dominions are much the same
So two Choirs for Worship and Two Choirs for Creation.
Virtues are an odd ball, Virtues are abit like personifications. The Scriptures often personifies good characteristics, Humility, Wisdom. Virtues probably look after spiritual fruit and gifts, if they exist at all. I'm not completely convinced this choir even exists, but it is possible that these are the Host that whisper into your thoughts...you know when you think its yourself talking, and its not...Though again, I think that is generally the role of the messenger class. Virtues are an odd-ball
Powers and Principalities. These are Host which fight. These specifically are the Warrior Class you might say. They generally lurk around insitutions, and around Governments and stuff like that. When the Book of Revelation details Christ writing to the Angels of an appointed Church, its likely that its intended for an Angel of this Class
Archangels, this Choir is a pick and mix. Its not a type of Angel, its a Title. An Angel in leadership...so for Example we know that Saint Michael is an archangel...but he's also a Seraphim...there are only a few Archangels, and they probably rule over the other Choirs...for example as Michael is said to be the Host incharge of the Forces of Light, he Probably is incharge of the Powers and Principalities...more then he would be over those who just Worship...or those who create. Michael Fights...or more aptly, Wrestles infact...but thats a different story
Below that are the Angels who look after individuals and transport messages around. When Paul says that people have entertained Angels unknowingly...its probably from this messenger class.
Took you longer to read that then watch the video didnt it hahahahaha