AMD just announced the new 7k series even the low end of the product line is expected to have new architectures. So IMHO I would either wait one month for the fire sale of current AMD gpus and save money, or wait 2 months and have some serious bandwidth for the same amount of money you are going to spend now.
Do not buy AMD if you are going to go Xfire.
If you have to play a game the day it comes out dont expect drivers the day of the title release AMD is a once a month release for WHQL and BETA drivers.
Other than THAT, AMD runs cooler and is more reliable than Nvidia for long term, but who actually keeps a Graphics card more than 3 years.
I would personally wait for Nvidias new offerings in January.
Here is a great read on AMD new offerings.
http://www.brightsideofnews.com/news/2011/11/30/radeon-hd-7000-revealed-amd-to-mix-gcn-with-vliw4--vliw5-architectures.aspx
http://fudzilla.com/graphics/item/25088-amds-hd-6900-series-gets-a-price-cut
XFX Price cut. Awesome warranty