Depends on the games and how long you plan on keeping it
If it's just the games in your sig, a cheap RX 570 will perform fine and give the most value. If it's something you want for a few years that you plan on running new releases on, get a Vega 56. You can get blower ones for £200 or £237 for a strix if you shop around. It'll beat the 1660 ti and when undervolted you have a 2060 level of performance.
I plan on keeping it a while and will be playing a bunch of games, not just the ones in the sig (lol, old sig, should change it to division 2 at least

went for the 1660 in the end (components delivered last night), but i really do appreciate all the advice. If i was gaming at 1080 but at a higher refresh rate, i would have gone for the vega
