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"Better" just way too subjective. Hell, it's practically flame-bait.
They're both very good cards. The FX would probably edge out DX8 games and vice-versa for DX9 since the FX cards have PS2.0 issues.
Your best bet is to google reviews on both cards and read them all. You won't get a clear answer, but you'll have a much better idea what's going on. It's very easy to just start half a dozen threads and ask for black and white answers. It doesn't work that way, though. If you want to be spoon fed, you'll probably just get a spoonful of crap.
I really think the 9700pro and 5900nu at stock speeds are a toss up. I don't have any experience as to the OCability of the 9700pro but I know you an OC the hell out of a 5900nu and an OC'd 5900 will walk away from a 9700pro at stock speeds.