Ok, if you are in an area where the price increase is in effect, I CAN happily suggest the nvidia cards, as the price increase for the amd cards really hit their value.
the 780ti is faster than the 290x plain and simple while producing less heat and consuming a little less power.
the 780 can be overclocked to match the 290x in some games (at 1080p, as the 290x admittedly does very well at higher than 1080p resolutions).
if you can wait, then wait. If you were buying today, i would recommend the nvidia side purely due to the stupid price increase of the amd side.
don't expect pricing to change on the amd cards anytime soon, as they JUST released these new ones a few months ago, and the mining craze is still in its infancy (doesnt show signs of slowing this year)
the nvidia cards also recently underwent a price drop, so don't expect them to come lower any time soon either
august-november is when the new flagships should be coming out, but i wouldn't expect a super mega increase in performance. not to mention they will not be cheap
my personal hope is that amd decides to make mining dedicated cards, and then releases some really killer gaming cards. this would be the smartest move, as they would increase their consumer market by quite a lot.
nvidia is kinda meh, they can keep doing what they are doing as they for the last 2 generations have held the flagship single chip (titan vs 7970, 780ti vs 290x) but their stuff is so expensive that it hurts