GTX 1070 G1 OC $335 (Pre-owned)
GTX 1070 ti $460 (Pre-owned)
GTX 1660ti $410
RTX 2060 (475)
At your resolution (1080p), prepared a spreadsheet on straight performance versus dollars spent based upon TPU testing and rankings and accounting for the potential OC of each card. Some caveats involved.
1. The relative value of a card is much different for a used card versus a new card with regard to warrantee, efficiency, etc ... so it's unfair to compare the two value wise.
2. I don't know which brand / model cards are listed ... some cards are better performance, better fps, better cooling, lower noice, different efficiencies. For the sake of concictency and to insure a review of the same model existed for all 4, I used the MSI Gaming series cards
Overall Score = Summary Ranking of Reference Card in Latest TPU Review for 1660 Ti
Overclock = MSI Gaming X FPS Overclocked / Reference Card FPS
Price = OPs Listed Price
Relative Value = Score x Overclok x 1000 / Price
3. Used cards:
The used MSI 1070 Gaming had a relative ranking of 95.00% overclocked 10 %, a price of $335 which resulted in a relative value of 3.130
The used MSI 1070 Ti Gaming had a relative ranking of 109.00% overclocked 16 %, a price of $460 which resulted in a relative value of 2.757
4. Used cards:
The new MSI 1660 Ti Gaming had a relative ranking of 95.00% overclocked 16 %, a price of $410 which resulted in a relative value of 2.696
The new MSI 2060 Gaming had a relative ranking of 113.00% overclocked 12 %, a price of $475 which resulted in a relative value of 2.670
5. While the 1070 is the "value leader", given it's age (released June, 2016... 3 years ago) ... i wouldn't "go there". With the value of the other 3 being so close... the 2060 seems an easy choice.
File attached