When looking at different brands all you need to worry about is the 1)warranty 2)tweaks they've made to the reference design (overclocking, cooling, ect), 3)bundled items ....they are all almost identical in performance because they all have to follow reference design. Also keep in mind a warranty doesn't mean much if they don't honor it or make you jump through impossible hoops to get it, so do a little reading on customer satisfaction with the companies support before you fall for an "extended" or "lifetime" warranty.
just read up about the warranty on their website. Tigerdirect has a great 30 day no questions asked warranty, so if its doa you should be covered by them. But for your original question, any 5870 is going to perform the same no matter who it is made from, just make your decision on price and those other things I mentioned above.
yeah the warrenty is good but tiger direct takes up to 1 week to get your package out another site i went to takes up to 3 weeks!!! which is crazy im gonna wait till the 31st and see if newegg gets it back in stock
Currently, 99% of the 5870's are just branded stock models, as in nothings changed past the base 5870 ATI released, So go for a good warranty or supplied extras (Battlestations game from Sapphires stock ver. or HIS gives out a toolkit, XFX has the best warranty) Sapphire has a VaporX (aftermarket cooler) version of the 5870 on newegg, but it was quickly taken up and there wasnt any reviews on it the last I checked to see if its better than stock