I first used Charmander (in the Red version), because I basically fell in love with it while watching the early episodes of the anime (this was years ago, back when the anime first came out here). I guess that's where my love of fire Pokemon began. I ended up starting with Cyndaquil in the 2nd-generation games.
Although... I don't mind the water-type starters either. I could easily get a serious game going with Squirtle or Totodile, and I always start with Mudkip in the Hoenn generation games.