I have sapphire 4870 1gb and it's good. It also has rear exhaust but one a disadvantage I noticed is I'm not able to OC. It seems like even if I unlock the OC'ing thingy in CCC (and not change anything) I get artifacts so I would not recommend it.
Unlike the HIS 4870 1GB, the Saphire 4870 1GB - http://www.newegg.com/Product/Product.aspx?Item=N82E168... - actually has a split cooling solution, where 50% of the heat is exhausted from the rear of the case, and the remaining 50% of the heat is recirculated back into the case from the front end of the card.
I've actually heard nothing good about sapphire's cards. I would go with HIS if I were you.... VisionTek (or ATi, the actual house brand, although I don't think ATi manufactures its own cards anymore...) are the best brands. VisionTek is the only one that has a lifetime warranty on it I think, and they have good customer service.