Only one or two people mentioned something other than power... Any fan of the pkmn games would know that defense, speed and hp are just as important as strength, also, think about how much energy they can use all at once. Mewtwo is better defense wise, obviously, he's a pocket MONSTER, and not exactly a teenage human... Health, no clue. Speed, anyone's guess, but I'd say they're even. Tetsuo obviously has stronger powers, but as mentioned, he cannot control them... But if he DID manage to get out Akira's universe(to meet Mewtwo), doesn't that mean he would have control over a HUGE ammount of power?!
Prob with VS threads is that the idea is very complicated, but no one realises till some smart-a** shows up and mentions speed and defense. Oh, and accuracy! Mewtwo hits straight on, and Tetsuo misses sometimes. sweatdrop