Hm. Didn’t see this until it was too late to vote. Practically speaking, the round avatars on the sister sites don’t make much impact. Until I saw this poll, I didn’t even think about it.
But now that I have checked all 4 sister sites, I have to say, I like the square shape on BYC better, because it doesn’t cut out as much of the image. It’s hard enough to find a nice photo that looks good teeny tiny, without having to find one that looks good teeny tiny with the corners all cut out.
But, avatars are just icing on the cake. They are just a fun little detail, so not a crucial consideration. Well there’s my (more than) 2 cents worth.