If my memory serves me well, then at the beginning updates caused a lot of issues, but for past couple of years I'm pretty confident when doing updates. I update only via web UI when new version becomes available for my instance. Currently running v19 though v20 has been released 2 months ago. That way I believe I avoid some of the bugs when major version is released :).
Some negatives aspects that I have encountered, but don't see as a big deal -
newer Nextcloud versions require newer PHP versions that are not provided by Ubuntu LTS, that means, that I'm no really benefiting from LTS and I have to upgrade the distribution if I want latest Nextcloud (don't want to upgrade PHP separately).
and couldn't get Talk working reliably, whatever I'm missing, it feels that documentation could have been better.