I had a stock XFX 5870 working greatly for 2 years and gave it to a friend, now I have the XFX R7970BEDD (at 1100/1425) working also great. I needed XFX support for some questions, they were always great. I know, however, that many people over the web are very dissatisfied with XFX. My current 7970 works great, is cool and overclocks high BUT there are so many complaints about defective model. XFX has prices about 20% cheaper than other good brands though, so its your decision on this one.
If you have money to space, buy MSI, if you dont then try to buy a Sapphire or XFX.
Be warned though: XFX and ASUS high-end cards have voltages locked from BIOS in their latest productions.
Also, remember that an overclocked card like the MSI Lighting etc. will perform THE SAME as a stock card which you manually overclock, it is just based on luck if you can go much higher than 1100/1500 with a stock 7970 while it is much more likely that you can do it with a higher quality card. I'm saying that cause a basic 7970 costs £320 in the UK while the ASUS DCUII, MSI Lighting etc costs over £400 while not offering much more. "GHZ edition" cards at not any better than the older ones, they are just binned with higher frequencies, save a few coins and buy the normal edition then OC it, cause its the same card.
So why i went with XFX instead of MSI for the 7970? well cause i liked the orange/brushed alluminium looks (awesome compared to plastic) and my mobo is orange coloured...