The 5970 is faster than the 295 so if you want the fastest card and ya have $625, the 5970 is the way to go unless you want PhysX. If ya don't know whether ya want PhysX read this and decide if it's worthwhile to you.
http://www.firingsquad.com/hardware/batman_arkham_asylum_physx_performance/page2.asp
http://www.tomshardware.com/reviews/batman-arkham-asylum,2465-11.html
If those cards are too expensive, fix on your budget and then look here:
http://www.tomshardware.com/reviews/geforce-310-5970,2491.html
Here's the "winners" from THG's latest (December) GFX Roundup
Best Graphics Cards For The Money: December '09
$50 - HD 4650
$65 - HD 4670 / 9600 GSO
$85 - 9600 GT
$95 - 9600 GT / HD 4830
$110 - GTS 250 512 MB
$120 - GTS 250 1 GB
$155 - HD 5770 / GTX 260
$200 - HD 4890
$240 - 2 x GTS 250
$310 - No winner (HD 5850 Honorable Mention)
$330 - 2 x GTX 260 / 2 x HD 5770
$400 - 2 x HD 4890
$410 - No winner (HD 5870 Honorable Mention)
$465 - No winner (GTX 295 Honorable Mention)
$625 - No winner (HD 5970 Honorable Mention)
Note that card prices have risen lately due to shortages.
As it says in the article tho, if ya gonna keep GFX card more than 2 years, DX11 will provide future proofing if DX11proves significant.