which GPU better for ....

you should go ahead with amd in the first place, all upcoming games will be optimized for amd anyway.
just check nextgen consoles, all of them have amd gfx inside. therefore almost every game developer will focus on amd.

For that price, probably a 7950.

On a side note, why don't you just do some research yourself?

get extra 50$ and buy a gtx770