My recommendation is if you can find it for the right price, then buy it. Cause right now AMD cards are hard to find. At the same time the GTX 1060 is a good card for $250, but only for $250. I wouldn't pay anymore than that for a 1060. At the same time I don't believe in needing anymore than 4GB for the RX 480 or 470. You will rarely reach beyond 4GB with these graphic cards, though there are some games that make good use of the 8GB of VRAM.
Personally the sweat spot is RX 470 4GB, but that's my opinion. Because of the less Compute Cores, the RX 470 can be overclocked easily. For $150, if you can find it for that price, it gives the RX 480 and 6GB 1060 a run for their money.
I haven't seen benchmarks of the 3GB 1060, but at face value I would avoid it. $200 for a 3GB card is just wrong.