newer gen. GPUs are generally better if you can afford them, newer features newer architecture and so on. first of all what is your CPU and full pc specs? you wouldnt want to upgrade to a beefy grpahics card then not able to run it properly.
and lastly id suggest the GTX 1070, its faster than the GTX 980 Ti and would probably be cheaper ( i might be wrong but here in my country the GTX 980 ti is more expensive than the GTX 1070, some have the GTX 1070 cost more than the 980 Ti so yea).