GeForce GTX 550Ti or Powercolor Radeon HD 6670 Crossfire with AMD A10 5800K

What will give me good performance a Powercolor Radeon HD6670 crossfire with AMD A10 5800k or a GeForce GTX550Ti?

I am doing gaming and a bit of editing here and there. 



CPU: AMD A-10 5800K

GPU: Powercolor Radeon 6670


RAM: 2x4GB 1866MHz Corsair Vegeance 

PSU: Antec 500W 80 Certified 

CPU Cooler: Stock AMD A10-5800K

i think if you're getting another 6670 i would say that would likely be better than getting a single 550 ti, but it always depends on what you are doing, some programs are not optimized for crossfire, and that would hurt your preformance, but also if you buy a second 6670, you would likely get it for a better price than the single 550 ti.

Well it is being given to me by a friend 

then there is no doubt, although it isnt all that great, and you can get a pretty amazing gpu for like 100 dollars, if your friend is just giving it to you, then take it.