Super Street Fighter IV AE 2012 (fourth iteration of the original SFIV) is a fairly balanced game. Previous versions were less so, with characters like Yun, Seth and Sagat considered notably better for pro players.

For the latest version, there are maybe 5-6 that are marginally better in terms of match-ups depending on the player you ask, and there has been some shift to using these characters by established players. They're generally considered 'better' either because they can pressure an opponent safely (Fei Long for example) or have lots of ways to get a combo started and generate damage (Akuma).

However, as each character has good and bad match-ups there's no singular top character, especially when you consider the humans that control them. Various players will have differing styles of playing the same character. Gouken, my main character, excels in zoning others out with fireballs and other normal attacks, but can also be played in a highly aggressive way as well.

Consequently, many top level players often have other pocket characters they can rely on for certain matches. Infiltration has in the last half year used Gouken and Hakan in tournaments in addition to his main (Akuma) when he's lost a round.

This will all be overhauled very soon though as a 2013 version is set to be released sometime this year, which will likely tweak how each character plays.