1070 Ti is faster and has more VRAM so it would be the better option if you get it at a lower price.
If you're not in a hurry you should wait for a couple of months for the mid range 3060 and Ti to launch, going by the 3070 it should be priced $350-400 which would be a better deal than either of those cards at this point of time.
Even if 3060 goes out of your budget you might find sweet deals on used gpu's once it launches.
With all the bells n whistles that come along with 1660 Super, the end of the performance is inferior to a 1070 Ti. However, you will end up paying more for a 1070 Ti, how much are you getting it for?
I am myself gaming on 1660 super on a 1080p res and I find it adequate, so my suggestion is to go for 1070 Ti if your budget allows or stick to 1660 Super and it will still solve your purpose.
But the best option is to wait for a month.. let the RTX 3070 and Big Navi cards launch and that will lead to prices of these cards to go down and you can get a sweeter deal. Also, the market will be flooded by really good second-hand cards within the warranty period