I'm inclined to say square. Some people still haven't received Sheogorath's Breaking News, and now they can't even see who is declaring the Cheese or who the Cheese is for! The Daedric Prince of Madness is outraged at this happenstance and demands immediate compensation in the form of square dances, flaming circles, and the splein of the Destroyer of Worlds.
Get this man a medal I think he solved the issue. If people like round they could just edit their square ones.
Most avatars in existence are designed to be square. Because square means, a bigger canvas for the artist. It is why you see so little round paintings, maybe oval ones, but then its stretched a lot.
they could just put a blank background then. Square is beeter though, because like you said, its alot more work to do that, and if we keep circle, everyone that has stuff cut off, has to change it.
They too are possible, if we have square avatars, someone can make theirs into a triangle if they want. Man, square avatars sure give us, the users an awful lot of creative freedoms. I am so glad we have those.