All of these brands have to adhere to ATI standards in order to be able to market their products as HD Radeon cards. There are many brands and some may offer extended warranty over other brands, some may offer slightly more features, some may offer more packaged games, but in the end they are all the same. The technical differences between all these brands are negligent, so I would base my purchase decision on price and their reputed service/guarantee name.
I usually go for the cheapest price myself.
Go to Newegg and read the reviews... not only how many EGGS are given, but WHY someone gives a good or bad review