I've noticed it definitely varies depending on how you access it. The web version is flawless as long as the software has the resources it needs to run (my server is slightly very over-provisioned and gets crazy IO delay pretty frequently from running too much on too little).

The official Android and IOS apps are pretty good but do glitch and hitch from time to time, but apps on other platforms are less perfect. Also the third party Streamyfin and Swiftfin apps both seem to work a bit better than the official one but have their own quirks to be aware of.

The Roku app only just got consistently usable around 3-6 months ago, and still prefers to crash without displaying an error when fed media it can't direct play, and for some reason some user profiles just don't work on it. I don't have anything else to try other apps on but that's my experience so far

I haven't really used Plex so I don't know how clean of an experience it provides, but Jellyfin is very usable and honestly at this point most of the problems I have are specific to my media or my setup and not so much problems with the software itself