RSE: In Ruby/Sapphire I always choose Torchic. I think I've started Sapphire once with Mudkip, but I always liked Torchic's evolutionary line. (Blaziken4Life.) In Emerald, I've chosen treecko. I finally could have a Grass type with nice speed and offensive stats. Also, Leaf Blade.
FR/LG: I've played Leafgreen first, and chosen Squirtle. In FireRed, Bulbasaur.