there may not be a best martial art, but tkd is the freaking worst.

I would vote for tennis or swimming for my personal preference, as both seem to give a full body workout.

boxing, you will always need to know how to punch good :)

Dodgeball. If you can live through a game of dodgeball while keeping your pride intact, you'll probably be able to survive just about anything.

Knowing how to swim will help prevent you from drowning, but martial arts are good for self-defense..