Absolute Anime

Out of them all I think torchic is the best.

I typically start with fire types since in the games I own (basically all the gameboy games up to Firered so I don't know anything about diamond and pearl and i'm assuming Firered Leafgreen are similar to the originals) you don't get to catch fire types until later on. Also because fire is my favorite element But it is pretty hard to start with a fire type in Red/Blue since you first battle Brock and Misty where using fire types isn't quite the easiest out of the 3 choices.
But in Ruby and Sapphire was it just me or was battling with Torchic a pain? It seemed that for any gym battles or trainer battles my torchic had to be several levels higher than treeco or mudkip had to.. But in Ruby/Sapphire my personal preference is Mudkip since
1)It's really cute
2)It's ground attacks are great against it's weakness (electric types)

I always start with Grass types. In the first game, I started wtih Bulbasuar, and breeze my way through the first three gyms since their attacks weren't very affective against Bulbasaur. Chikorita even breezed through the second Gym, but that was because we trained hard and I taught it poison powder before we reached Falkner.