Sapphire is by far the better brand. They build quality products and are the largest AMD graphics card supplier in the world. Powercolor is relatively new and isnt as big. Both will work great but if you have the money, I would choose Sapphire.
Powercolor isn't new :S they've been out for like 15 years.
Powercolor make inferior boards and have been known to cut corners. Their electronics don't bring the same quality most others do and you will probably be looking at a 15-30% performance loss compared to the top cards.
Well, I have a PooperCrapper R9 280x, and judging from my Fitestrike mark, and other peoples Firestrike mark that also have a PooperCrapper, it performs poorly, even OC'd to 1200/1600, I'd easily say it's around 15% under performance range from the top tier cards. I bet the lesser models such as R7's would be even worse.
PooperCrapper are cheap for a reason, their cooling isn't the only thing that's subpar, they've even been known to put in half the bus lanes needed for the bit rate in cards years ago.