I'd definitely choose Microsoft Lumia 950 XL.
Why? The right question would be "why not?"!
I've had only Lumia phones since they came out, my first one was the Lumia 800, a small but strong phone. Then I had the Lumia 1320, when I first saw it, I thought it was too big to be loved, but as I kept using it, I discovered its functions and advantages, even more with the WP8.1. Since then, I've wondered how could I live with a small screen size, now I can't imagine my life with a very useful large screen. Finally, I bought the Microsoft Lumia 640 XL, this one has been amazing. I can't stop loving the phone, the screen, the OS, everything.
The main thing that kept me on this devices was their camera, completed with the Lumia Camera app. The most wonderful cameras I've ever used, and complemented with Lumia Creative Studio they are just unstoppable.
Now, since the first time I read the first news about a new Lumia flagship, I searched for all information I could get. That's when I fell in love with the Talkman and Cityman. As time passed by and new pictures and specs came out I became even more and more excited, my only concern was what would their prices be. Nowadays I cannot believe this beautiful phones are almost here!