Would definitely not recommend KDE Neon. It’s more of a showcase of new KDE features than an actual usable OS. I currently use Kubuntu and it’s fine. I wish it updated more frequently but the update frequency isn’t slow enough to really be a deal breaker.
I disabled snap Firefox, not really because I’m ideologically against snap, but because snap Firefox is annoying to use. Other than that, the OS generally just works out of the box.
I’ve heard good things about OpenSUSE, but I’ve never tried it. My personal opinion is that I want to stick to the most common distros so that it’s easier to find troubleshooting advice
Yes, you can add the Mozilla ppa and they offer a non-snap version. I think the Deb that you download from their website also isn’t snap, but I haven’t tried it