I feel all the Kanto starters are great and all equal in terms of overall usefulness throughout the game. Squirtle holds the slight edge, because it was my first.
Just my opinion. Totodile is balanced and crunch helps with Morty's gym.
Mudkip 25 %
It would be an even 50-50 if we were talking Ruby and Sapphire, but because of Emerald and wallace as champ, Treecko becomes very useful in emerald.
The 10% is all based on design. Not a great generation of starters. I would prefer not to use any of them really.
Another just ok generation of starters. Serperior is the best looking starter evolution ever, but a terrible pokemon. Oshawott line is awesome, but the Tepig line is a huge fail for GF, IMO.