Fedora is RHEL’s officially unofficial little brother. I had to go to Ubuntu on account of Fedora’s feverish upgrade timelines. I was happy to see Canonical doing LTS on Ubuntu distros. That makes me happy.
That being said, I’m sort of on the fence with Mint. They’re a decent distro, but I’ve become such an Ubuntu fanboy that I can’t imagine going to another flavor.
I do support KDE but prefer Gnome.
Ubuntu releases just as often as Fedora--twice a year. The difference is that while Ubuntu's LTS is still called Ubuntu, Red Hat's LTS is called Red Hat--and Fedora remains the semi-annual update. While Red Hat does charge for their flagship, CentOS and others do release their copy fairly shortly after RH releases.
Mint is still mostly based on Ubuntu... Even this Mint KDE has Deb AND Ubuntu repositories...
I do love Ubuntu, so stable