Dragon Ball Z budokai 3
That game along with super smash brothers+halo2+mario kart were the main multi games played in my boarding school, and personally budokai 3 and ssb were the ones I enjoyed the most.
Budokai 3 though... Played that so much and since I always played with my favorite character, yamcha, it was like playing with a permanent handicap all the time.
Eventually I just started raping with him

Yamcha would win all the tournaments, defeating kid buus and gokus and vegetas alike, and when I had a real challenge, i'd switch to a more powerful character and be unstoppable ^^
Honestly, i'm so confident at this game I'd gladly enter tournaments for it and be reasonably cocky of winning the whole thing. There is no other game I can say that about.