Usually when comparing Corsairs and XFX, it comes down to how long their warranty is and which one is cheaper. Case being that both are very close in design and manufactured by seasonic so build quality most of the time matches each other.
In this case, the XFX is cheaper after rebate compared to the corsair which means its the better buy.
Some of them are, the HX series is actually built by Channel Well Tech, but both are excellent units and very similar in results for ripple, voltage regulation and efficiency, in a choice between those two i would go for the cheaper one because you cannot really lose. The only thing that bothered Wolf about the 850W XFX unit was the glowing green fan, they have since gotten rid of that so now it would end up with an even higher overall score than the HX 850.