To those saying it is pointless to wait for Vega, you're overlooking two things. First, there is a plethora of Freesync monitors out there, including the recently announced 27" 1440p VA 144Hz ones from Samsung. Freesync monitors often cost around $200 less. More importantly, the distance between them and the G-Sync selection is only growing by the day.
For someone who is already a Freesync user or is planning to become one, waiting for Vega makes sense.
Secondly, DX12 performance on AMD is stronger than it is on NV in this generation. So even if 1080 is stronger in DX11, if you're planning to keep the GPU for 3+ years, AMD could make more sense. And I say all this as someone who is happy with my current 980 Ti. I'm personally waiting for Volta and whatever AMD is planning to release to counter it(Vega+?) and then make up my mind.