It depends, if the 7x rx580 is cheaper then it's worth going for than the Nvidia build, you need to consider how much your electricity bill costs because the AMD rig will draw more power but future proof the 8GB RX580 wins.
The Ellesmere RX 400/500 cards will not be future-proof. They are only good at ETH, which will become irrelevant after PoS. After PoS, Nvidia cards will be the best since they perform well on multiple coins. The other problem is the RX 580's won't be efficient. Efficiency will really matter after the PoS crash, since revenues will crash and power cost is much more important. If you reduce power cost by 20%, you can probably make 20-30% more profit. Even if your strategy is to mine & hold, you'll be able to stick to that strategy for longer if the power bill is lower. Finally, these cards are 5-6 years old, so it's very likely a lot of them will fail at that age.
I don't like the GTX 1660's or any card with < 8GB or VRAM. Some algos benefit or require 8GB+, and new coins will probably be built with larger VRAM in mind. The 1660 isn't that efficient as well.
I think if you want to build a rig now, the best choices are the RTX 3060 LHR, RTX 3080 LHR or RTX 2070S/2080. The LHR won't matter because ETH will be dead. Even if you mine ETC, LHR is great at dual mining, so you can earn as much as an FHR card that only mines ETC. LHR cards will fall less in value than FHR (& especially AMD) after PoS and they're backed more by the gaming market.
After the PoS crash, newer AMD like the RX 6700 or 6800 might be decent because they're OK at non-ETH algos, while probably being very cheap and having decent efficiency.