I always liked XFX because they had the coolest boxes that they sold their cards in. The X-shaped box was on my shelf as a trophy of pride for a long time when I bought my 7600GT.
I like XFX for the warranty they offer and customer service they provide, short of that I would build a system around this beast and get rid of my old Tandy machine.
The 6990 is almost crazy overkill for the gaming I do, but XFX is the company to buy a Radeon from. I am growing weary of the green card I am running and want to go back to red, so I'll likely have something XFX pretty quick without winning any drawing at all. Go go superior warranty and support!
I like XFX because of their relieability, warranty, style of cards for custom builds, and out of the box performance increases. The 6990 is an incredible card as well.
I choose XFX for their double lifetime warranty . It makes upgrading easier when you can sell a card that still comes with a warranty . Plus the black and red color scheme looks cool .
I used to stay away from ATI (AMD) cards because I hated the brands that made them. However, since I love XFX (currently have a xfx gtx 260) I would love to have the 6990 in my system. Pretty sweet when your "brand" makes Nvidia and ATI cards
For past few years I mainly buy xfx's card, it is sad to see they walk away from Nvidia, I am not a fan of Nvidia, I just buy what I need, so I jump between N and A. But anyway, xfx has great customer service. They response to my GTX 260 RMA within 24 hours back in 2009. When I buy a GPU, I always go for xfx one first.