1660 is on par with the 590. 1660 Ti is faster. Other things to consider is freesync/gsync compatibility if your monitor supports this technology, power consumption, heat, noise. 590 is power hungry whereas the 1660 runs chill
The 1660 is the better choice. Unless absolutely wanting to have a AMD card, there's no compelling reason to go for a RX590 at the same price while not offering better performances but drawing more power thus generating more heat and noise...