Hm...let's see, somewhat because of appearance:
Kanto: Charmander and it's evolutions
Johto: ...I'm leaning toward Cyndaquil, but I haven't really played 2nd gen.
Hoenn: Definitely Torchic and its evolutions
Sinnoh: Piplup and its evolutions
I guess the Fire-type is one of my favorite types, but I probably chose Piplup as my Sinnoh starter in the game because...appearance, maybe? Plus, when I figured out that Empoleon had only three weaknesses, that was kinda a bonus.