For R/S/E, Mudkip all the way. Once you get Marshtomp at level 16 and start integrating Ground-type game, it becomes much more fun. (Mud Shot! Wattson didn't know what hit him.)
For FR/LG, Bulbasaur! First two gyms were easy, and by the time I got to the third and fourth, I already had a Fighting-type and a Flying-type to take care of them. It just worked.