I have the Gigabyte Windforce OC and it overclocks nicely. I have no complaints and have not had to deal with any customer service so I can't really speak to that. The Windforce is a great cooler - the EVGA model has no aftermarket cooler and since both cards are about the same price I can't help but recommend the Gigabyte for the superior cooling performance and added overclockability related to the cooler temps.
It has a custom cooler with 3 fans, and it also is in contact with the Vram. It has five power phases (one more than the stock cards) and has a gtx680 pcb. When overclocked it will attain performance levels of a gtx680, and will keep the card cool. Note that the MSI gtx670 PE does allow for overvolting which will get you better overclocks. The advantage that the evga ftw card has, as someone has mentioned is the great customer service, but it does have a stock cooler.
If you want a reference card then evga is the way to go.
If you want to push a higher overclock, then I would go with either a gigabyte windforce, asus direct CUII (get the non-top and then overclock it yourself), or the MSI PE. The non reference cards are generally better performing, run cooler, and use better components which means they should last longer.