All I've ever owned was ATI's (now AMD).

First card was a Radeon 4550, then a Radeon 6450? (I believe it was), and now I have the R9 270. I can say nothing but good things about radeons. Nvidia I am just not a fan of because it's either super quality and terrible performance or the other way around in my passerby experiences with the cards. I hit anywhere between 400-700fps on CS:S on completely high settings (they are totally maxed out).

40-60 for in World of Warcraft on Ultra - no lag.