Good day Yeltzin.
This a question for the ages. It's based on such a wide range of factors. It is not a question that can be answered in one word. But here is my humble opinion.
If you have the money for the 980ti, go for it. This card will last you for a very long time. Even the 980, which is cheaper. If you are considering the 970, then I would also consider the AMD Radeon 390. I know, I know, a lot of us vouch for NVidia but, the 390 beats the 970 and it is cheaper and it has 8 gig's of RAM... so just consider it and look at the benchmark.
So that's it. I would consider the 980 if you have the money or the AMD 390 or NVidia 970 as the second option. I am a NVidia fan but I am considering the AMD 390 for this coming Christmas (since I don't have the 980 budget).
Cheers,
G.