Rock, Phychic, and Lightning are definitely unique, but when I choose my first pokemon, a lot of the decision is based on how cute they are. Since there aren't that many cute Rock/Phychic pokemon, I'd trust my chances with the Grass/Water/Fire ones more.
Then again, some people worry about pointless things like how strong they are, and Phychic pokemon are pretty strong
Soooo I guess in the end.. maybe letting the player choose would be the best idea.