No GPU is worthy getting now as they are all waaaaaaaaaaaaaaaaaaaaaaaaaaaaay overpriced and no one really knows when they'll go back to stock prices...
Best option is wait or try to get a used one.
For a decent upgrade, get a GTX 1080, as the jump to a 1070 wouldn't be soooo much IMHO. But there's little point in getting a 1080 if you only have a 1080p monitor...
Basically,
GTX 1070 for a nice upgrade. 1080p 144Hz
GTX 1080 for a great upgrade, 1440p and above.
Or if you really got the cash, the 1080Ti.