Basically they all give the same performance.
There are two versions; one with 512MB and another with 1GB of VRAM. The HD 5670 is really too slow to make use of more than 512MB of VRAM so there is virtually no difference in performance. Basically at the very best the 1GB version would give at most 2 extra frames per second at high resolutions.
Pick the cheapest one with the best warranty. If they all are only one year warranty then pick the cheapest.
I would choose the following Sapphire HD 5670 1GB since it is the cheapest (after a rebate) with free shipping; total ending price of $55. Sapphire's parent company is Athlon Micro. They are an OEM (original equipment manufacturer) who manufactures video cards for other brand name and slaps the appropriate sticker on those cards.http://www.newegg.com/Product/Product.aspx?Item=N82E16814102930