Well, I use a lot of characters, but my Abel is very clearly the best one I perform with and I use Sagat, Seth, and Cammy for his bad match-ups (Bison, Akuma, and to lesser extents Zangief, T. Hawk).
There are a lot of things I disagree with though. For starters, the game is still awfully unbalanced and I think charge characters break way too many match-ups. Of the 10 new characters, 3 of them are actually good. Some characters were intentionally made to be bad (as said by Ono) like Dan/Makoto and he also said Capcom intends to make Sagat top tier in every game. On top of that, Capcom straight up lied about some of the changes they've made. I suspect Super was created by chimpanzees because, despite everyone's disagreements, they still kept in selectable Ultras which will and probably already has led to the same thing as Street Fighter III. One Ultra is going to be better than the other in almost all areas for almost all match-ups and the other will be eclipsed into nothingness forever. Also, counter Ultras are ridiculously terrible.
Vanilla SFIV is even worse for balancing and the only reason I would go back to it is if I really badly wanted money with how broken Sagat is.
Despite my complaints, I still have fun.