The 750ti is a stronger card than the r7 360, so that would be the better choice for gaming performance. You still won't be getting anywhere near ultra at decent FPS with the 750ti with those titles, however.
You'll need something like a GTX 970 or AMD R9 390 to get really good FPS with those titles on ultra, and those cards cost quite a bit more than the GTX 750ti and R7 360.
That said, you can youtube the GTX 750ti with games like Witcher 3 and see that people ARE able to play them, but don't expect smooth gampeplay at high settings.