If you can find one for a good price, the Vega 56 is a really good card, good enough that nVidia was forced to bring out the 1070ti to compete. The Vega 64 cards are harder to recommend unless you don't care about power usage. Either way, you will want an aftermarket card from ASUS, Sapphire or XFX as the reference cards cooler isn't very good.
Below Vega, the RX 580 is the better buy. Again, if you can get one at a good price.