i have great computer but my GPU is very very low .... so i wanna buy new GPU one that can hold all games with great FPS and great quality in-game ......... i found two option : one is the
Nvidia 660 Ti .... or the other option :Nvidia 590 Dual Core on spec the 590 is much better but im afraid that he will not support crysis 3 or any heavy games ..... can you tell me what is better or even suggest about something else?

so or nvidia gtx 660 ti 2gb
or ....nvidia gtx 590 with 3 gb and dual core
or if you have any suggestion about other GPU please replay

ATI 7950 better.

GTX 670-136fps

ATI 7970-166fps
Both at 1200 MHz.
ATI 7950 not much less than ATI 7970

It is not rtr.

The GTX 590 is a dual gpu card (= SLI). It has a way better performance than the gtx 660ti. The 6xx series has its advantages but it's not necessarily better.
I would rather recommend you a single gpu card since you don't seem to be versed with hardware. Sli often causes problems and it's usually more comfortable to use a single chip card.
In that case I would recommend you a gtx 670. It's not as strong as the 590 but should handle all games without any problems.
The 660 ti is a good card and cheaper than the 670 but since you considered to get a 590 you should get the 670.
In fact you could get a GTX 680 straight away if there's no price limit for you.

You will not need more than this for the next few years. If you are willing to deal with SLI and itss problems you should get a gtx 690 or a combination of 2 cards (2 670s,2680s,...)

About AMD/ATI...
Cheap cards with a good performance but they can't reach nvidia cards. At least not the latest models. They're missing some things that nvidia has got like CUDA (not important for gaming)or physix. Similar to SLI they have something called Crossfire (cfx). It makes even more trouble than SLI so if you go for AMD/ATI take a single chip card.