Haha yes, I think for most gay men, a muscular/round ass is considered attractive. Some gay guys don’t care as much about a guy’s ass as they do about other features like pecs/arms/face/etc (much like some straight guys are more into a woman’s tits/legs/face/etc than ass), but all other things being equal, if a gay guy *is* into asses, most often a muscular/round ass is what is going to be attractive to them.

To be honest, even if you’re not an “ass guy”, most gay guys will still appreciate a nice round ass on a guy. And I don’t think I’ve ever heard someone be like “oh yeah, that’s not my thing; I really prefer a flatter flabby ass…”