The first time on Ruby I picked a Mudkip, who is now fully evolved and lives on my Sapphire version. On the second and third time around I choose a Treecko.
Torchic. The fire-type starters have always been the best. *massacred* But seriously, out of the three rather bad-looking (final forms of the) starters, Blaziken is better. Torchic, Mudkip and Treecko are cute, Combusken is bleh, Marshtomp has an icky Sugimori illustration but a good ingame and EX: Emerald art, and Grovyle is leet.
Treecko on Sapphire, because I'm copying my first Emerald team, and I had chosen Treecko on Emerald, after I restarted. Plus, Treecko is one of the best pure grass types.