Which 7950 is best?
If you plan on OCing the card then I would advise against the Gigabyte card due to the fact that most if not all Gigabyte cards are voltage locked. So you won't be able to OC much, if at all. Now that MSI card on the other hand is a good card and from reading the reviews people have been able to OC it, but what concerns me is that lots of people are complaining about bad quality thermal paste being used. If this is the case, then this card would probably have problems with temps at high OC's.
I honestly would go with either a Sapphire Dual-X/Vapor-X card or the HIS Iceq x2 card. All in all it comes down to what matches your needs and wants, and if your willing to pay more or less for a good card.
Personally I would not get ether of them. For AMD/ATI GPU's I would only get cards from Sapphire. I have these http://www.newegg.com/Product/Product.aspx?Item=N82E16814202003 cards for my Crossfire 7950 setup and they have worked very good.