in order:
mudkip --> treecko --> torchic
mudkip: mudkip is strong against lots of types, especially when it evolves. when it becomes marshtomp, you can best wattson easily and you dont have to worry about a grass gym leader, because there isnt one ;)
treecko: most of the trainers in the game are water trainers, and juan will be easy to beat if you have treecko. when it evolves into sceptile, it can be strong against lots of pokemon. wallace would easly knock out a good sceptile with ice beam on any of his pokemon though.
torchic: blaziken may look tough, but its fire/fighting duel type gives it more weaknesses o_O;; juan, winona, tate and liza could beat it up easy as pie.
so mudkip is best for me. and im not saying that just because muddie is my favourite pokemon ;)