Here is what I tried so far:
1) Dell XPS 9370 Developer edition: This comes preloaded with Ubuntu and it is actually amazing that everything works out of the box. It was too small for me though, and the fan made a rattling noise so I decided to return it. The 4K screen is probably overkill on such a small display. Based on the review people recommend taking the normal screen, it saves a lot of battery and there is not that much difference.
2) Lenovo X1: I didn't like the feel of the Keyboard, and the screen was not that good. Installing Linux (Arch) was easy, but decided to return it.
3) Dell XPS 9570: I have this one for the last two weeks and so far I love it on the hardware level. I would even put it as somehow superior to my MacBook Pro. The downside is that Linux is not well supported at all. I have installed Arch so far and spent all my evenings trying to fix all the drivers. So far: The Nvidia drivers are barely working, ACPI needs a lot of tweaks (but it seems I got it working and got my 7 hours of battery). I still need to work on the Touchpad, and couple other things.
So far, the Dell XPS 9570 is a good challenger to the MBP, but installing Linux is still going to be a small challenge