This is related to the anime (if that's aloud). So we're at the finals in the Kalos League (Ash in the finals?!? Not to mention he actually has a 50-50 shot at winning?!? WTF?!?). Regardless on paper who do you think has the better team between Ash & his opponent/rival Alain?
Greninja (Ash-Greninja, it's a Mega-Evolution but at the same time it isn't).
Charizard (Mega-Charizard X)