both are good companys and i still have my xfx 7900gs and i loved it. It overclocked pretty good too.
Evga offers a step up program where you can trade in the card for a better one and only pay the difference of the two prices, so if heys looking to upgrade later (within 90 days of the purchase of this card), then go for the evga.
If not then both companies are top notch.
CPU: e6600 @ 3.2ghz
RAM: 2GB G.Skill HZ PC6400
Mobo: ASUS P5B Deluxe
GPU: Sapphire HD4870
Soundcard: Creative Labs X-Fi XtremeGamer Fatal1ty
HDDs: 250GB WD + 750GB WD + 2x1TB WD
Monitor: Samsung 226BW
PSU: OCZ GameXStream 600W
Case: Cooler Master Stacker
OS: XP Professional SP3
Mouse/keyboard: Logitech MX518/Saitek Eclipse II
Speakers: Logitech Z-2300