A brief review of the Dell XPS 13 as a Fedora laptop
For years, my work laptop was a series of old second or third hand Thinkpads, I believe first a T40 and then a T61. These were relatively bulky and heavy, with short battery lifetimes (about two hours from full charge) and only a 1024x768 resolution screen, and their CPUs were both so old that they were 32-bit only machines. It's been clear for a while that 32-bit machines are on their last legs (Chrome no longer supports them, for example), so late this summer we decided to replace my laptop with a new 64-bit one. Partly based on my work from late 2016, I opted for a Dell XPS 13. I installed Fedora on it with my usual Cinnamon laptop environment.
I'll lead with the summary: I'm quite happy with my Dell XPS 13 laptop running Fedora. Everything works and using it is almost as pleasant an experience as I can imagine using a 13" ultrabook to ever be (given the limitations imposed by the physical form factor).
The physical laptop is a dramatic and drastic change; going from the heavy, bulky Thinkpad to the ultrabook Dell is a night and day shift. The Dell is much thinner and far lighter, enough so that it's quite easy to carry around relatively casually. The battery lifetime outlasts meetings without blinking and is easily good enough that I no longer worry about running out of power if I don't take the power brick with me. We got the basic FHD screen, which on the Dell's display is now enough room to fit two terminal windows side by side with more than 80 columns in each. The modern CPU, standard NVMe SSD, and 8 GB of RAM make it fast enough for sysadmin things that I don't particularly notice any big issues, even when doing things like starting Firefox (it's not instant, but it's a lot faster than the Thinkpad, which was, well, leisurely). The XPS 13's trackpad and keyboard are both okay but not exceptional; they're certainly usable, and I'd probably be better with both if I used the laptop more often. I'm still getting used to using two and three fingers for middle and right mouse button clicks and scrolling and so on, instead of having physical mouse buttons and dedicated areas of the trackpad on the Thinkpad.
(When I use the XPS 13 in its 'home' location, I connect up an ordinary USB mouse and use it by preference. If I was significantly using the laptop at multiple places, I would probably try out one of the portable Bluetooth external mice.)
Fedora (first 26 and now 27) has just worked on the Dell XPS 13. There are a few glitches, but these aren't the fault of the XPS 13 specifically as far as I can see (sometimes they're my fault). My Fedora Cinnamon setup has changed the trackpad behavior a few times in irritating ways, but that's been fixed with a visit to the settings system to re-set my desired trackpad options. All of the XPS 13's hardware appears to work under Linux, including special keyboard function keys. Certainly things like wireless and some USB Ethernet adaptors have just worked (I've wound up switching between two for reasons).
The overall result is a laptop that I can imagine taking somewhere and doing productive work on for an extended period without feeling particularly confined or restricted (although it's never going to be as nice as my desktop, with multiple screens, a nice keyboard and mouse, and so on). The screen size and resolution is one important aspect of this; I get much more productive when I can fit two real terminal windows in side by side (with readable font sizes, or almost have two 80x20 terminals arranged vertically.
(As a result of actually being willing to do reasonably serious work with my laptop, I've been discovering that Cinnamon has a bunch of handy window management key bindings. I wish they were all documented in one spot somewhere.)
I don't have any grounds for an opinion on whether the Dell XPS 13 is the best Linux ultrabook you can currently get, since I've only ever used one ultrabook (and my XPS 13 is now one generation back, since we bought it back in August). I do think it's a decently good and decently usable one. If I was buying an ultrabook for myself, I would default to getting some XPS 13 version unless I ran across a compelling reason to do otherwise.
(For more demanding usage, well, I can't imagine running virtual machines on it, but I do build Go from source every so often, more or less just because, and I have some Go stuff on the laptop that I poke at every so often. It runs Emacs and similar things fine, too, but that's not really surprising.)
PS: The one thing I wish for in the XPS 13 is more USB ports, especially USB 3.1 gen 2 USB-C; mine has two USB-A ports and one USB-C one, which isn't really enough once you start wanting to attach a mouse and a USB Ethernet adaptor and so on. I imagine that more USB-C ports will come in time, hopefully not at the expense of the current USB-A ones.