Wait for the surface. Windows 10 mobile isn't stable now. If there will be a surface phone it will be a fantastic one with superb hardware features. Microsoft may release Redstone 2 along with it which will be much stable and will have lot of new features.
Lumia 950 is pretty good. But you should remember that there are other, newer, phones out there.
The expensive ones (because we are comparing with 950):
There is the HP Elite, which is pretty expensive, but everything seems better than 950 except perhaps the camera and size (I prefer smaller).
There is the new Alcatel, which also has better hardware than 950 and also a good camera it seems.
As of right now, the Surface Phone is only a rumor. Nothing more. If you sit around waiting for a device that may never come, you'll be waiting a while. If you get a phone now, you can enjoy it now.