Depends how old your GFX card is & how much 3D support you need.
If your card is recently new (r500, r600, r700 etc) & if performance is your #1 consideration then go for the closed source ATI driver & their stack.
If you have an older card or if you're happy going with open source solution then you're best off finding something that's tracking Dave Airlie's work. That's being pushed into Fedora (in "mesa-dri-drivers-experimental"), but i think other distro's are re-packaging it.
I'm running the bleeding edge experimental drivers from koji on f12 with a 4870 dual screen & it's working really nicely.
TBH, you're best off going searching around in the Phoronix forums for an answer.