it's like that: Some games are better optimized for AMD, other games are better optimized for NVIDIA
at the same price it's a stalemate, difference is pretty close, in dx12/Vulcan the Rx480 is a bit better
usually the 1060 is the better deal as all 1060s perform around the same while it pays to buy a more expensive Rx480
that being said the MSI Gaming X is a really good Rx480 and if it's that much cheaper than a 1060 it's an absolute no brainer.
if it was the other way around and the 1060 was 25$ cheaper it would be a tough choice, but like that...get the Rx480 before it's out of stock