Re "Files" speed
Ubuntu 16.04 running on a Core i5 with nVidia graphics vs. Raspberry Pi 3 with Raspbian/Pixel: I find the file manager on the Pi (PCmanFM) to be much snappier than Files on the Core i5.
I appreciate that there's less thumbnailing enabled by default on Raspbian, but even so, I struggle to understand how Files manages to be sooooooooooo slow!
As for Ubuntu/Unity, I've stuck with Unity thus far because, it's good enough. I like some Canonical stuff, like all the polish with colours/icons/fonts, but it's always disappointing how many bugs there are... it always feels like Canonical don't dog-food the LTS releases, so they get pushed out but the user has a ton of work to do to make them usable. ¯\_(ツ)_/¯