Honestly non-reference designs are almost always better but if you're ready to buy you should go for it. The reference design is pretty good, if a bit loud at load. Either of the cards you mentioned should be fine- I personally have more familiarity and comfort with XFX but I wouldn't shy away from the VisionTek if it was a better deal.
Longer warranty is a good deal for you if you plan to keep the card longer than 2 years. The peace of mind goes a long way!