Does it really matter that much what distro it ships with? As long as the laptop ships with any distro preinstalled that hardware tend to be properly supported by the Linux kernel, allowing you to feel safe about installing any other (up-to-date) distro.
I've got an older dell laptop that came with Ubuntu 12, bought in 2013. I assume everything worked back then, but I needed Windows for school.
Some months ago, wanting to switch, tried Ubuntu 14 and Debian 8. Couldn't get the graphics driver to work on either. Proprietary drivers, other than the ones in the Ubuntu repos, required a mismatch of older/newer library/kernel versions which I couldn't figure out how to get in Ubuntu. The open source driver claimed my hd7670m worked, but in reality I was getting the hd4000 performance out of it.
Everything else worked, a bit noisier though. Either way, I would definitely not feel safe when buying another Linux laptop, proper research is still required.
Unity is default, not only supported desktop environment. I haven't tried all availalbe environments but getting rid of Unity for xfce is just `apt-get install xfce4`, and it's the same for more exotic options like xmonad.
I tried latest Ubuntu (after using many other distros over the years), and I'm perfectly fine with it. The GUI is simple and does all what I need, with useful default behaviour.
