For the titles you have mentioned, a 960 or its equivalent will be more than enough.
If you're at least looking to play aaa titles (the witcher 3, crysis 3) with all max settings at 1440p, then the 980 and 980ti will be up for consideration. And if you're looking into a 980 and a 980ti, money would normally be a non-issue. The 980ti would represent the better value over the 980.
980ti uses GM200, similar to a titan X, whereas 980 uses GM204, similar to a 970. The 980ti has an extra 2gb v-ram over the 980, which will come in handy for future aaa titles at higher resolutions, and for sli. And it outperforms the 980 by 20%, while nearing the titan X in terms of performance.