Despite the massive amount of bashing going back and forth here, I feel compelled to point out that I've swapped back and forth between both AMD/ATI and NVidia over the years and I've run into problems with brand new games having glitches with one or the other on both sides. Even having said that, I'm talking two or three times in over a decade. Aside from that I've had fans go out on one card, and it still lasted long enough after that that I didn't feel bad when it came time to buy a new one.
For most people it really doesn't matter what card you get as long as it isn't ancient. For enthusiasts, compare specs and get what you need. If the specs look like they're in Klingon to you, take the time to learn what's what. If you can't be arsed to do that, then you aren't an enthusiast in the first place.
This isn't like rooting for your home sports team. There is no justifiable reason to give complete loyalty to any company when weighing your purchases.