The RTX 2070 is a little bit faster but way more expensive than the 1080. However it seems to be a little more future proof. If I were you I'd wait for 2-3 months when the GPU market will become more competitive with better prices. AMD will introduce its new GPU line-up in the near future and Nvidia will likely be forced to drop its prices. Also the previous gen cards will be out of stock by then which may force prices down, even if the new AMD GPUs aren't too competitive.
Finally I think it doesn't worth upgrading to a 1080. The performance difference isn't too big between your current GPU and the 1080 and it isn't really a 4K GPU. It's also a 1440p GPU that is able to reach higher fps numbers than your GPU in current and future...