In my experience, every group has a different overpowered character for every game. Peoples play styles are just to broad to properly nail down an overpowered character. When going from high school friends to collage friends, it seems that every character that was overpowered was considered weak, and vice versa.
Not only that, but my research project for my Psychology degree might shed some light on this situation. I found that people were more apt to win a game when they were confident in there abilities, and felt like they had a better chance. So a person picks their favorite character, and wants it to be overpowered. Then, they are more likely to win, which increases confidence, and a character becomes over-powered from the positive feedback loop. Or you lose against a character you think looks overpowered, you lose confidence, and its a downward spiral from there. Ive actually used this phenomena (Social facilitation) as a strategy before. In Capcom Vs. SNK 2, a friend of mine was absolutely unbeatable with Sakura. At this point, no one had used Sagat very much. So I made a decree that Sagat, regardless of how good he was, was tailor made to defeat Sakura. Sure enough, the Jedi Mind Trick worked, and to this day, Sagat almost always beats Sakura, regardless of the respective players skills.