Those Lucario-replacing-Mewtwo fanboys are really annoying. Mewtwo is, by far, the best pokémon (the other pokémon are prescindible scum). No, Lucario's not cooler, he's a blue dog with shorts; and a generic pokémon.
Why not both?
I don't support Lucario (in fact, I hate him), but he's popular and the most recognizable 4th gen pokémon, so he should be in. BUT, Mewtwo is the most recognizable legendary pokémon, and it's one of the most popular pokémon worldwide. Both of them should be in, along with Jigglypuff. That's 5 pokémon reps.
Pikachu as the face; Trainer as the main protagonist; Mewtwo representing the Legendary pokémons; Lucario representing the non-1st gen pokémon and Jigglypuf... is cute.
Oh, and the Pokémon Rival is a bad idea. Pokémon Trainer is awesome because he's the most unique fighter ever (even more than Ice Climbers and Olimar). Two trainers is a bad idea.