In my opinion the 6970 is the only other option besides the gtx 570, Its about the same price and about exactly as poweful as the 570, they both beat each other by a little bit in every different game, (I'm assuming your gaming?) Overall i think the 570 is slightly more powerful then the 6970 from what i've seen. But its pretty much even, and they're both about the same price. The ati is a higher wattage than the 570, doubt that will affect your choice, It's pretty much which company you trust/prefer, if you play games with physx, you should go with the nvidia since it can run it. There are other little things like that aswell, but overall either one is solid.
Also there is no way this will be a quick question, there will be tremendous amounts of epeen and fanboyizm being thrown around here.