Which is better?

[albinalex]

Is a gtx 960 sli better or gtx 970.Will they run on my vs550 watt corsair supply?

 

[Coolboy951]

i would recommend going with one 970 due to having more memory.

 

[Andrew Murdoch]

+1 970

 

[joshlane]

Is a gtx 960 sli better or gtx 970.Will they run on my watt corsair supply?

Dual 960 will offer more power than a single 970 due to the ramgate issue but a lot of games don't support SLI very well meaning that they would be running on only one card.
From what i can find on you PSU it looks like it would be able to power two 960s or a 970.

Personally i would run a single 970 due to the issues found with SLI

 

[maddogfargo]

+1 for the GTX 970

Crossfire and SLI can be a little buggy and will never offer 2x the performance for 2x the price.

I recommend going with the best single GPU that you can afford.