although the crossfired 290's do give better performance, its not by more than 5 maybe 10fps. But the 770 sli will run quieter, cooler, and consume less power by a fairly large margin. Nvidia also has better driver support and smaller things like shadowplay and game streaming.
SO performance alone, the crossfire 290's. But performance still held high and better all around, sli 770's. I have sli evga superclocks gtx 770's in my pc, and love the fact I don't need a 1000+w psu to supply them, nor do my ears ring from fan noise since my rig is right next to my monitor.