Before we go any further, know that this information isn't scientific. It doesn't even come from Capcom. But it's still interesting, so, on we go! Event Hubs have posted a chart outlining - based on the Japanese arcade release of the game - which Street Fighter IV characters they feel are better than other Street Fighter Characters. Their methodology? If two players of equal skill play each other ten times, how many wins would each character rack up?
Like we said, it's not science. But if you're one to subscribe to the notion of tiers in a fighting game, here's their data: Poor Vega.
Street Fighter 4 Tiers — Character Rankings [EventHubs, via Capcom]