You could go with a Nvidia FX 128mb. What ever the best one is or an ATI 9800 Pro128mb, you'll mostly be wasting money for the extra 128mb, but it's up to you. For battlefield I would go with an Nvidia for the same reasons Bonez pointed out. Nvidia works better with Battlefield.

Though if you want to do flight sims than you would want an ATI.
ATi is better with flight sims
Nvidia is better for FPS games and especially EA games.