I've already chosen kung fu, because I like the logical basis of it. The movements, the goals, the thinking, everything makes instant sense to me, without needing explanation. It just seems instantly practical for fighting, rather than all the mystical BS that some schools like to give you. That may just be a function of the teacher, though.
And to be fair, I have very little experience with the others. I've tried aikido and left after 2 months because I hated it so much (incredibly slow pace, unintuitive movements, didn't seem like it had any practical use) despite all the good things I'd heard about it.
edit: next on my list to try is jui jitsu, and I'd love to check out muay thai eventually as well. Most of the martial arts intrigue me, actually.
edit2: capoeira is really cool. I saw a demonstration once, it looked like a lot of fun (and hard work!).