I would vote for the GTX 970 all the way! But, as much as I HATE to say it the new R9 390 cards are giving the GTX 970 a run for their money.
https://www.youtube.com/watch?v=k9cKZiJw6Pk
The AMD Cards run hotter, use more power, and have less updated drivers (last stable AMD driver was December 2014). Furthermore, the R9 3xx series are just re-freshed R9 2xx cards and the R9 2xx cards are re-freshed HD7xxx cards. So overall, AMD has not got much "new" to add for a while.
Also, the GTX 970's in SLI perform better than the GTX 980 Ti or AMD Fury X Cards. Get a single GTX 970 now and go GTX 970 SLI later when the price drops and you need more power.