I think quaterbacks can be seperated into two seperate catagories. There are those who are only as good as the offense built around them, and there are those that create plays, or in other words, they make it happen. You put Kurt Warner on the Bengals, he will likely fail. On the flipside, if you threw Favre on the Bengals, although any playoff hopes would likely be out of the question, he would have much more success then Warner because he is a guy that can build an offense of his own, in that he will make players around him better.
I can't say for certain where Warner fits in, I havent seen him play for anyone but the Rams, but when you look at his numbers last season, it kind of gives it away.