I would not recommend using Clear Linux as a desktop Linux choice. It more of a specialized thing especially for Intel equipment and on the server side more than anything. It is fast. Yes you can use it, with some work as a daily driver, but I would not make it a first choice for anyone.
Ubuntu and Mint are not simply two different sides of the same coin. Ubuntu and Mint both will have some of the greatest support out there for anyone wanting to get into Linux. Ubuntu has many desktop environments to choose from. The base directly, from Canonical uses the Gnome desktop, however You can choose XFCE from Xubuntu, Lxde in Lubuntu, KDE Plasma from Kubuntu, Ubuntu Mate, and so on. It’s going to be what you are more comfortable with. Ubuntu Cinnamon is also trying to get into the group, but is new.
Mint is based on Ubuntu, but handles some software installation slightly differently, like pulling only required things to run what you are installing, rather than required plus some recommended packages on top of it like Ubuntu does, but this generally isn’t a problem in daily use, meaning, you won’t notice. Mint has three desktop environments to Choose from; Cinnamon, XFCE and Mate. It is based only on Ubuntu Long Term Support, so major upgrades come once every 2 years, security updates and patches continue for up to 5 years, minor point releases that include improvements from the Mint team every 6 months or so. Software can get a bit dated, but then that’s when you start getting into using Flatpaks for things that are newer.
Out of these two, Mint is generally the first place to start, unless you like to get into things a bit, and then Ubuntu is fine as well. Mint just provides a few more ease of use items in its software.
If you are really adventurous, I would recommend, yet hesitantly, to give Manjaro a look. Arch based while not being arch, rolling release and stable, at least in my experience, and a large amount of software. Again, this is probably something I would recommend to someone comfortable with tinkering or has used GNU/Linux at least a year, just so you have a base understanding on how the OS works.
All Linux distributions use the Linux kernel, perhaps just a different version, but they are all GNU operating systems at their heart, and follow general guidelines, command structures and directory structure. Package managers are the things that differ the most.