My first of FRLG (and my first pokemon game at all) was Leaf Green, and I chose Bulbasaur. Then I played through Fire Red with Charmander. Then I traded the nice stuff out of Fire Red and replayed it with Squirtle.
My first of RSE was Sapphire, and I chose Mudkip. Then I played Ruby with Torchic, then finally Emerald with Treecko. That's one thing I loved about having three games to a set - three games and three starters equals one for each.