I actually like Ardour's GUI a lot (and am grateful that it uses Gtk: KDE never ran stably on a machine I owned, and I found that in Gtk-based environments, it is actually always the Qt applications that are inexplicably unstable). The main problem that prevents me from using it is that I keep running into show-stopping bugs in the backend: for instance, MIDI recording (including even "loopback" where I just recorded the output of another MIDI automation channel playing in Ardour itself) in 5.12 kept dropping note-on/-off events, and more critically, there is some persistent issue that results in ZynAddSubFX plugin settings getting corrupted through save-load cycles. I have confirmed that the latter is still around in 6.0, and the furthest I have gotten in pinning it down is the observation that the correct state seems to get saved in a plugins/<id>/state<n> folder, but this is not what gets loaded and loading and then saving again without doing anything else results in it creating a state<n+1> subfolder with the garbled state without state<n> being touched.

I haven't had any luck getting responses to bug reports, and anyhow it seems that ZynAddSubFX should be a sufficiently common plugin that if this bug were easy to reproduce, someone else would have stumbled upon it by now (and so it probably arises due to a weird interaction with something else that's particular to my setup).