Some years back I was using testing. It was the year they changed over from Gnome 2 to Gnome 3. I couldn't use the stable release because my mainboard and cpu wasn't supported.
Boy, was this a hard process. It took some months until my system worked without GDM crashes. After that I changed over to Arch and been a happy Arch-er since than. I wouldn't recommend running testing.
I've heard that unstable is more like Arch linux and the rolling release model of Arch Linux works very well for me.
I've been running debian on an x1 carbon as well (gen 3). I was impressed that it 'just worked' to the point that I even got an inbuilt wireless modem, popped the SIM card in, and the only bit of configuration I had to do was, literally, choosing which of my ISP's APNs to connect to.
I've been running stretch on a lenovo carbon x1 for the last 2 years and it's been one of the first problem-free experiences running linux on the desktop (linux user for.. 18 years). Really awesome. Thanks!