GTX960 is significantly faster than 750Ti, but the price of a GTX960 is also way over priced comparing to GTX970 that's about only $50 more than 960. If budget is a consern, 750Ti or 950 both are good choices at below $100 and $125 respectively for 750ti and 950.
If you want high end performance at best return per dollar, GTX 970 or some AMD cards will run much faster than 960/950/750Ti .