Future Trunks is probably my favorite character; Gohan was alright as an adolescent until he started putting on the 'Sayan Man' crap; Piccolo has been steadily a cool character, if somewhat useless (seems Goku, Vegeta and all these other guys get to do the important ass-kicking. Piccolo seems mostly reserved for blowing up the moon and such other trifling chores.)
Vegeta's alright in fights, if not for the fact of him being such a constant butt-head who eventually gets a swift kick in the ass.
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Oh wait, the cat. I change my answer: the cat is certainly the coolest character.
