Well, Sapphire and PowerColor are top tier AMD partners, I don't think you would do wrong going either way.
But I can tell by own experience, having a Red Devil Vega and liking it soo much I decided to give a go with the Red Devil on the 5700XT, I would VERY surprised as I already had high expectations, the card feels solid, good build, it is whisper quiet and with realy good temps so far the best card I ever owned.
Personally I love the RGB on the card, the Devil logo looks awesome where Sapphire implementation is a bit more shy.. Also the shroud of Sapphire cooler is plastic..
Again, either one it's a great card.