They are pretty close. Either is better for an individual depending on some variables i'll list below. What games you play is also important when choosing.
GTX 1060 6GB:
- Lower Power Usage
- Generally Lower Temps (Better cooled)
- Better Performance in
most Nvidia GameWorks titles, DirectX 11 and OpenGL games.
- Mostly the stronger card at the moment on
average
- Excellent Overclocker (If that interests you)
RX 480 8GB:
- Slightly cheaper (Most the time)
- 2GB of more VRAM
- Better Performance in
most AMD Gaming Evolved titles, DirectX 12 and Vulkan games
- CrossFire (Mulit-GPU) compatible (If you would consider this)
- Appears to be getting stronger over time thanks to driver optimisations and patching, this will likely make the card a better long term choice, See here > http://www.hardwarecanucks.com/forum/hardware-canucks-r...
To summarise, the GTX 1060 6GB often comes ahead in most games today and with lower power usage + temps at that. However many things on the RX 480 would indicate it to be better card in the long run due to the extra VRAM, better driver support, better performance in newer APIs (Vulkan and DX12) and of course the ability to add another RX 480 in CrossFire (you might see one cheap). Just a final note, the RX 500 series isn't far away so i recommend you consider waiting for that to drop before making a decision. Just go for whichever card has features that appeal more to you and your build. Hope this helps