Now it's time for the verdict :) Remember this is purely from my point of view as someone who travels 200 days a year and does presentations for living. This is just my opinion.
I'm trying to review features that really matter to me. It's easy to say that both are superb devices compared to many others as the 3000$ price tag would suggest.
For more specific figures and values read this: http://www.notebookcheck.net/Dell-XPS-13-9350-InfinityEdge-Ultrabook-Review.153376.0.html
I totally agree with it and it gives the common performance numbers that I've verified with the great (Finnish) PCMark tests.
Size with Accessories = What I need to carry
The Dell XPS is way more beautiful and compact. Seeing them next to each other I would easily choose Dell. That's not the whole story anyway when it comes to what I need to carry with me. I sit in the airplane and I'm usually first in the plane because I'm a priority passenger and I want get a place for my trolley. This means I sit in the airplane more than others and have more time to watch series before the seat belt light goes off. This time I need a tablet and Dell XPS won't do. This means it doesn't work by itself but I need to carry my Surface 3 etc. with me to be able to use it while the flight ascends or descends. With the SurfaceBook I'm good. I'll turn the keyboard under the screen and if someone still complains I just put the keyboard away. It's a very big screen so I am missing my kickstand to be honest. That's something I'll live with or buy a kickstand.
That's for the device itself but that's not all. I need a USB hub and wired network. That goes for both and the external devices for this are the same sized. I need DisplayPort adapter for the SurfaceBook. The one I have is from StarTech with VGA,DVI and HDMI. With Dell I need the USB 3.1 extender but it has VGA, HDMI and Ethernet. It only has one USB port so I need the Hub anyway. So both require two devices which are of equal size and weight in total.
I need Biometric readers to authenticate. With the Dell XPS this only means a thumb size USB fingerprint reader for my personal use. It doesn't take space but looks ugly. And it only allows me to authenticate but not to demo Windows Hello's Facial Detection. For this I need an external camera. With the SurfaceBook I'm good to go as it has the needed camera for both my personal use and demos. SurfaceBooks battery lasts twice as long for me as the XPS does. With the XPS I can get through flights but only with the Power Companion from Dell. So SurfaceBook is bigger but with Dell I need these extra things to carry with me: Powerbank, RealSense Camera, Fingerprint reader. The ones that I need to carry for both or are of equal size are not listed, like external SSD, power supply, mouse and a wireless presenter.
Working with the computer = What can I do with it and how well
Keyboard and touchpad on both are good. The only problem I have is the US keyboard on the Surface which really does heavily bug me. Performance is good enough on both though SurfaceBook beats basically every aspect and the SSD and GPU performance is WAY better on the Book. Now when it comes to presenting there are a few things that differ. SurfaceBook with the DisplayPort adapter has never failed me - it just works. Only thing I need to do sometimes is to change resolutions. XPS on the other hand only fails me :( The HDMI-adapter hasn't worked on any of my external screens without using Intel's application to set frequencies etc... The VGA I haven't tried on either one. For me the quick and easy use of external monitors and projectors is of huge importance. The next thing I need to do is draw on the screen while presenting. I bought this to work with the touch screen of the XPS at all: http://www.adonit.net/jot/pro/ I highly recommend it if you don't have an active digitizer - it's very good compared to any other I've tried. Now I can't rest my hand on the screen, I can't erase, I can't select and I don't get pressure sensitivity. All of these I get with the SurfaceBook. This is honestly one of the biggest differences for me between these two. To do my work I like to do it I need the Surface 3 as a companion for my Dell. Well I need it for the travelling time as well on the other hand. But getting that picture to show from two devices during a presentation - that's not always that easy. Next I need to run VMs. If you've read my previous blog you know how it works on SurfaceBook as well and I can say both run just as fine with nice SSDs and 16GB of RAM.
Fun and spare time = Which one I like if I don't need to worry about work
The Dell is awesome on the lap! Both have equally good speakers and screens. I'd rather have the XPS on my lap but honestly the battery runs out too soon for my liking... I like to sketch and draw sometimes so Dell won't do it for that either. And OH BOY do I hate the webcam placement on the XPS!! I knew I wasn't in perfect shape and have gained a few pounds but the XPS really makes sure I understand the seriousness of the situation... The webcam is situated in the lower left corner of the screen so it looks up to you below your chin and you have no contact what so ever with your family while on Skype...
I know SurfaceBook has it's faults and I do hate the wrong keyboard layout but for my work the choice is actually quite easy at the end of the day: The XPS has to go! SurfaceBook is a keeper :)