Maybe wait and see what happens with Mantle. We have been led to believe that its release is going to be this month for BF4. If what AMD said about it being 'up to 45% faster' with Mantle then deffo get AMD. But if they remain silent on Mantle then go with Nvidia, at least they delivered Physx and G-Sync.
Also I recently got a Sapphire R9 290. But they have ran out of BF4 codes and have said they have no idea when they will get new ones which peed me off. Also I signed up for Sapphire Select Club (Gold Member) and they have no offers, free game promos or in fact anything else they tell you that you can get for signing up. They literally get your email address and thats it.
If you go for an R9 290, maybe consider this Gigabyte one:- http://www.overclockers.co.uk/showproduct.php?prodid=GX-133-GI
It comes out of the box with non-reference cooling (Windforce), a high clock rate and a 3 year warranty!!!