If you look at the nine choirs of angels beginning with the Seraphim and go to the ninth choir you will see it listed as simply as that Guardian Angels, they follow the Archangels. So that is their choir.
That we have personal guardian angels is not de fide but would be rash to disbelieve given the support among the Fathers. (1) We are guarded by angels; guardian angels are the closest to us of the nine levels of angels (3x3). Angels guard nations as well, and these are probably higher categories of angels. St. Thomas gives the accepted arrangement. (2) Here is an angel work-sheet to test your knowledge.
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