What graphics card do you have now?
The 1660 Ti is another card to consider, with a price and performance roughly in-between the regular 1660 and the RTX 2060, and very similar performance to a 1070 on average. The GTX 1070 is no longer being manufactured and it's price when buying new is typically higher than a 1660 Ti, so I would not consider paying more for one of those than for a 1660 Ti. The 1070 has a bit more VRAM, but the 1660 Ti has newer architecture that should perform a bit better in newer games.
The RTX cards also feature some hardware acceleration for raytraced lighting effects, though its so far only been used by a few games, and causes a big hit to performance when enabled, so it's yet to be seen how useful it might be.
As far as each card's performance compares, each level of card tends to push around 15-20% higher frame rates than the one below it.