Online, the RX 580 and the 480 are said to be the best choice for mining, however, after some research it becomes clear that there are better options. So what should you go for? Well, the 1060 seems like the card for you.
The 580 costs around ~330$ on amazon and generates around 2.3$ a day using nicehash, this translates to ~144 days (as of 23/12/2017) to break even without considering the cost of electricity or the price of the other parts.
While the 1060 6GB version costs around ~300$ on amazon and generates 2.84$ a day using nicehash, to break even it would take only ~105 days (as of 23/12/2017).
Although, when it comes to stock power consumption the 580 with 150w outperforms the 1060's 180w. Depending on where you live this might me a big deal to you, but for most of us even with the higher power consumption the 1060 would still remain the better choice.
Here are the exact hashing speeds for each algorithm with each gpu:
The AMD RX 580 4GB
NVIDIA GTX 1060 6GB
Sources: