"Áo quần" and "Quần áo" are the same. They are used interchangeably and nationwide.
The collocation is identical to my language (Khmer): khao av (pant shirt) = clothes = quần áo
Is "ao" a classifier for clothes, or is there not a classifier for clothes, because I have seen "cai" more. I was wondering because shirt, coat, and clothes all use "ao."
As I understand it, ‘áo’ means a shirt or top. It's in the word for a shirt, of course, and it's also in the word for a coat, since a coat is a top. Finally, it's in the word for clothes, because that word literally means ‘pants [and] shirt’.