Best bum??
Well, one that isnt bony for a start.
But, one that is thrust into the air, cheeks pulled apart, clean hole, and the girl says "please, finger my pussy and eat my arse until i cum"
Have never really been into anal sex tbh, take it or leave it really, but Ive always had such a thing for rimming women, find it sonerotic, probably the naughtiness of it i think.