Whatever is cheaper, pretty much the same card...
Depends on your gaming resolution.
I'm using 1920x1200
GTS 250 and 9800GTX are pretty much the same card....if you have a small case then GTX 250 would be better.
Shame your PSU isn't a 650/700w GTX 260 out performs both and is similar in price.
Also, if you go for a PNY model, $50 off any of the cards listed here with the coupon code if someone hasnt already used it:
http://www.computerforum.com/152902-coupon-code-newegg.html