Debian
I'm interested in using Debian on my next laptop. The releases are slow, of course, but not much slower than Ubuntu long-term support (LTS) releases. For a few years now, I've been using Ubuntu LTS, anyway. I've found that many non-LTS releases introduce problems on my machine. Besides, these days, it's not hard to install newer desktop applications using Flatpak and newer CLI programs using… I don't know, Homebrew and language-specific package managers?
Debian's commitment to free software would have appealed to me more as a younger person, but these days, I want a laptop that just works, and I do see the value of proprietary software. Apple creates great software, for example, and it very often has higher usability and user experience standards than open-source software does. (Liquid Glass and the iPhone setup process are notable exceptions over at Apple. Signal, WordPress, and GNOME, among others, are notable exceptions in the open-source community. Also, I really hate the way Apple behaves as a company, but I think that's largely a separate issue.) Thankfully, with Debian, it's easy to work around the free software guardrails and install proprietary software. So easy, in fact, that the FSF faults Debian for it.
What's wrong with Ubuntu LTS? Not much. I like it, and my gripes are pretty minor. Ubuntu does have a habit of force-feeding their users unpopular software that was built in-house, however, like Unity, Snap, and lots of other stuff. I would prefer a pure GNOME experience. Plus, I think it would be fun to learn Debian. That's probably the main reason I'm interested in switching.
Maybe some additional thinking will change my mind, but at the moment, I'm interested in giving Debian a shot. I probably don't have enough energy or interest to do it now, though. I'll wait until I buy a new laptop. (I remember installing Arch Linux mid-way through courses at RIT and being unable to use my laptop for one week while I figured out how to properly configure full-disk encryption with LUKS and dm-crypt. Yeah, those days are gone.)