Im a ass guy myself
Posted under General
Not very picky with women so I'd go with Ass.
Boobs can be vairying size and are a product of genetics, way too much focus gets put on them since in sex the most you can really do is squeeze or caress them, which is ok if you're into sensual play but I'm more of the rough type.
Thighs are good and can be trained in the gym to be better however they only really work on girls that are average male height or tall at least for my tastes, i'm yet to see a petite girl with watermelon crushers and have that look good.
A nice ass can be genetic or achieved through hard work, works on all body types and can be used for all types of kinky shit, you can also leave a handprint on there to make sure everyone knows she's yours :]