i mostly bottom, and for me it's about pleasure. i've topped a few times and never really liked it. the feeling of a cock on my prostate to me is better than my cock inside an ass.
I mostly have sex with women, but strangely enough i prefer more dominant positions with women, i don't know why lol.. by dominant i mean doggy style, missionary, spoons, etc. i think it's about a feeling of dominance and feeling good that they're feeling pleasure at my mercy, so to speak.