Single card AMD drivers won't give you much grief at all, and quite a few crossfire owners have no to few problems at all.
That said, after running a GTX 480 for a while now I have to vote for Nvidia this time around.
The 570's price point is right, the features are there and the horsepower at stock speeds are there.
Overclockability is just added icing on the cake.
oh...and 3d, should you ever go for it, is just plain sweet.
Just my humble $.02