Well, for me, this is easy:
950 is not the best looking, but it has the best spec for now.
Surface phone will be top notch in 8-10months. But:
Well, it's possible they will not be ARM, so, somewhat really inovative for that form factor. Look at the first surface, and at the surface book, there were (and are, for the SB) lots of problems, regarding the build conception, or even the firmware/software. The first really amazing surface tablet for me is the 3rd, and I'm pretty sure the surface phone 2 will be a huge improvment over the first one.
So all in all, I prefer to have a good phone now, let the "test phone" be, and go for the second iteration of the surface phone, which in any case will be better than the 950 AND the surface phone of this year.
Now that I have the 950XL in my hand,I have no doubts I will keep it for two year, whatever the first surface phone will be.