Hi miner765

Well, measuring as usual, from my experience:
1. Price
2. new/used card
3. Hash-power
4. watts


So the winners are:
1. R9 270X/270, approx. 185 watts. Can be still found new. Nice hash(420 on average)
2. 7790. Almost perfect: approx. 85 watts and 220 kH. Fairly cheap, can be found new if u are lucky.
3. 7770 and 7750. I'd say those are just "for fun" nowadays. 80watts and approx. 170 kH.

There is a bunch of other older cards.

Mining on any Nvidia, except reported above is a LOL as per me, in matter of particularly ur question.

Hope this helps ya.