TBH , none !
I would say get a second 290 and Xfire if you already own one 290 and need more performance badly and now.
I would say get a 970 if you already have a G-sync monitor.
People tend to by pass the huge leap that we are going to make soon in the displays department, in Q1 2015 more and more display port 1.2a standard monitors will be out in the market.
Displayport 1.2a means an open standard G-sync basically , some people and Nivida themselves say they will not support the adaptive refresh rate open standard , buy many people are skeptical about that statement.
I would suggest putting your money in a much needed refreshing advancement on the display sector , adaptive sync is just a must.
If you go for the 970 you are buying a GPU that won't support disaplyport 1.2a adptive sync and if you will be forced to pay a lot for a G-sync monitor, not to mention you buy a GPU with no competition on the market , not even by its own series (the GTX 960) , and yeah the GTX 970 is clearly a great card but still I won't get it before you can compare and contrast it with some upcoming GPUs like the 300's from AMD or the 960 from Nvidia.
And for the 290 , kinda old card not that power effiecent , I won't get it , even if it is great value for money right now in the long run adding that extra buck for a newer GPU will pay off in the long run being more future proof and less power consumption in the power bill.
Just hold your money for now , I really think it's worth the wait , but if you cant hold it just keep in mind that that the monitor plays a huge role in your gaming experience.
TL;DR:
1) If you want to Select a GPU in a smart way , start with deciding on the resolution , refresh rate and adaptive refresh rate solution (if you want one) of your monitor, then decide on a GPU that will work best with your monitor.
2) Don't buy a GPU that currently have a "lobby" on the market (still no GTX 960 or new Titan from Nvidia or the 300's from AMD)
3) Don't buy old GPUs , not going to pay off in the long run ,in terms of power consumption, and not being future proof.