I like all the kids, because I love the whole "little kid can kick your butt" story. I loved Goku as a kid, then Gohan and then Trunks and Goten.
As far as villains, I'm a Frieza fan - simply because he was the first villian of the DBZ world (and the first I saw when I started getting into it).. Plus, his battle with Goku had much more tension to it because Freiza really did seem unbeatable (prolly cause the saga was sooo long).
Fat Buu is great too. I dunno, the more I think about it, its hard to choose a favorite. Vegeta's character went through the most radical and awesome transformation (although once he finally started being nice to Goku at the end of the series, I started missing the old cocky Vegeta)..
I liked Videl and Chi Chi, simply because I've always liked cute girls who could kick butt
Ah, and who could forget the Ginyu Force? Their corney poses were my kind of silly/dumb humor. I love that stuff. The best line was when he and Frieza were trying to figure out how to use the dragon balls, and Frieza suggests that they may need to use a special word - to which Captain Ginyu replies, "Would you like me to do the dance of special words?" I was laughing for like a half hour after that one.
Haven't seen any of GT yet, but from what I've heard it's terrible. My sister is collecting the original Dragon Ball series on DVD.. I'm enjoying that too.