A tough one for me this week. I went with Sandslash, Dugtrio, and Donphan.
Sandslash was one of the first Pokémon that I identified with in the RBY games. Dugtrio, I later found out in FRLG, was a fantastic Pokémon to start off with early when dealing with Lt. Surge. Donphan, I used quite a bit in Gold/Fire Red.
I guess I'll have to go with Dugtrio. Some of the pictures you find online of it are absolutely hilarious.