Syncthing has been much more reliable for me. It syncs extremely fast, picks up changes nearly instantly, and just works so well I never really even think about it.
Nextcloud has caused outright data loss once for me (all of my data was corrupted by nextcloud and then synced to my devices, had to completely recover from a backup), and broken due to updates several other times. It’s overall very slow, and a pain to maintain through updates.
what if I edit the same note from both places without internet and then both get connected to a network…
Syncthing will handle duplicates by renaming the older copy, and also has modes for versioning and deleted file recovery that you can enable and customized how you want to.