Well the two cards are not too much different from each other. The Sapphire one is slightly better in theory but in practise the human eye will not spot any difference AT ALL. Basically the difference is almost negligible. On the other hand though Sapphire is a more valuable choice than VTX so if I were you I would definitely go for the Sapphire one, since the difference is just 30 bucks!
Hope this helps!