Although I love the Dell hardware, I would go for the Surface Laptop in a heartbeat. The fact Microsoft tailored the hardware to it's OS themselves is a big plus for me. Also the design, the screen and the fabric used looks jawdropping to me. I would love to have one for music making on the road. If only I had about €1500 lying around...
If I were to pick between the two (I'm not planning to buy either of them, though), I'd go with Surface Laptop for a few reasons:
1. Battery life - the battery life claims of the XPS 13 (especially the touchscreen version) are grossly exaggerated. I tried one out and got 5-6 hours at most, after employees at the Microsoft Store told me it'd get 12-15...
2. Lighter, a little more compact, and
3. Looks. Looks shouldn't matter, but let's face it, people love something that looks good.
4. Webcam placement - not entirely a big deal, but that bottom up-the-nose placement on the XPS 13...
With that said, I probably won't get the Surface Laptop, anyway, mainly because of its lack of ports. I can do without USB-C or Thunderbolt, but they left out a MicroSD slot?!
I have used and bought for my company only IBM and then Lenovo ThinkPad's for many years but 18 months ago I bought a SurfaceBook Pro and I love it. It is fast, extremely versatile, and I love the screen aspect ratio. That is what we will be buying for now.
As far as for real heavy work and when I do real gaming my choice is still a good ol desktop workstation. Nothing like a pair of SSDs in RAID 0 and a pair or GTX 1080Tis in SLI
Since USB-C supporting Thunderbolt 3.0 is a big factor for me, I would pick Dell XPS 13.
If I have to buy a notebook NOW, it would be the Dell XPS. But if I could wait 6 months, then I'd get a Surface Laptop. Why the different choice based on time? My firsthand experience with Surface devices is to NEVER buy them within the first 6 months after release. There are way too many issues for me to trust the device as a daily driver.I'd like to know, if people had a choice, which one would they go for? Give a reason as to why you'd prefer a particular model - looks/price/features and what not.
It's interesting to see how people pick their laptops because not everyone is the same.
It doesn't necessarily have to be better from a neutral PoV but it could be what seems right for you, So shoot!