If you want overclocking the 7950's are much better and can perform even better than a GTX670 when overclocked depending on your luck in the silicon lottery.
For 660Ti's if you want good service get the Sig2, it has decent cooling and EVGA support, for pure performance, the MSi Twin Frozr will give great cooling and factory overclocks(they are no longer factory overvolted don't worry). The Asus one is great too if you want to do tons of overclocking yourself(cooling+custom PCB).