Gen 1: Bulbasaur. Ivysaur is one of my all-time favorite Pokemon. My favorite starter overall.
Gen 2: I love my Typhlosion so much. Even though I don't particularly like the species, I love my Typhlosion.
Gen 3: Probably Torchic. Blaziken is pretty awesome, and plus, Torchic is just so cute!
Gen 4: Piplup. It's the one that I chose, and I really liked it, even if Empoleon is sort of weird looking.
Gen 5: Snivy. Everything about it is just so cool! I love it's design and I love Serperior.