Personally I love the looks of the sapphire card and would go that way.
Edit to add personal experience:
I own an over 3 year old RX480 8gb Sapphire Nitro+. This card still works great and i suspect it will continue to live on for years to come. The only thing done was to replace the thermal paste.
I suspect this card had a hard mining life before I got it due to the low eBay price and odd vBIOS installed on the card when I got it. Still it continues to work fine
WHen I ran AMD/ATI mainly I always went Sapphire. I would say Asus would be my second pick there as Asus makes really good cards but Sapphire is known to be like the EVGA of AMD cards, some of the best.
Powercolor is sort of meh. They have a few but I would say Sapphire is a better overall brand than they are.
Yea definitely wouldn't recommend Asus. Between the two cards asked about, you really cannot go wrong, either way, based on the reviews. As far as history, of both brands, I would lean towards sapphire.