I am a little partial to nvidia however. I've always used them, and never had problems, so I have a little bias. Also, just about all the games I play are powered by nvidia. lastly, I have read that the ati cards have a lot of problems with driver updates.
I dont care too much whether it's an ati or nvidia board, I rather have 1 good card, so when they are outdated I don't have two old cards to try to sell.
So I would like to stick with the 9800 gtx+, unless someone can really convince me otherwise.