You've listed a GPU series. The 700 series is Nvidia's newest gaming series right now, read 'their best'. The 'power' of the cards gets better as the second number increases. ie. 70, 70, 70. Ignore the third number, it's filler.
The 770 is one of the best cards on the market right now. The 760 is a great card and an easy pick for price over performance. The 750 is new and was designed as an option for those with only a little money to spend. The 760 is the BEST card for price over performance comparisons but can't hold a candle to the 770. The 770 is more expensive but much more powerful. Both cards are great. If you can afford the 770, go for it.