Sapphire has about the best AMD gpus overall, as pertains to avg performance, reliability, service and support. Gigabyte is most often at the very top, performance wise, but usually at a cost in price, heat and fan noise, but is usually shadowed closely by both Sapphire and XFX. While XFX cards are generally sound performers, what hurts sales some is the plain-Jane looks when compared to the flashier designs of other brands.
Generally speaking, any of the 3 would be good, I prefer the quietness of the Sapphire and it's support dept, even if XFX return warranty is better (too many hoops to jump through)