Both Nextcloud and ownCloud plug in the same office engines. OnlyOffice, Collabora and the format question explained - and why the editor choice is separate from the platform choice.
Ask which platform edits documents better and you have asked the wrong question - neither platform is the editor. Both connect an external office engine through the same WOPI protocol, and the menu of engines is nearly identical on both sides. The editor decision is real and important; it just is not the same decision as the platform decision.
OnlyOffice uses Microsoft OOXML as its native format and presents a ribbon interface your staff already know from MS Office - documents round-trip to clients and government portals with the fewest surprises. Collabora is the LibreOffice engine in a browser: superb with OpenDocument (odt, ods, odp), complete and powerful, converting Microsoft formats on the way in and out - usually invisible, occasionally visible on heavily formatted files. So: a docx world points to OnlyOffice, an ODF world points to Collabora - and this rule holds identically whether the files live in Nextcloud or ownCloud.
Both engines have genuinely free community editions that small offices run for years - this channel's OnlyOffice series is built on one. Paid tiers buy support, scaling and enterprise polish, and OnlyOffice's free edition has historically carried connection limits that changed between versions, so read the current terms before designing around them. What neither platform gives you for free is the hardware: budget the office server its own share of RAM and CPU, or every editor comparison becomes a slowness complaint that was never about software.
Whichever platform and engine you choose, the pairing is a living connection, not a one-time install. Platform updates and editor updates arrive on separate schedules, and the connector between them occasionally needs a version bump of its own - an admin who updates one side blindly on a Friday evening will eventually meet a Monday morning of read-only documents. The discipline is boring and identical on both platforms: update the platform and the office server in the same maintenance window, test one real document with two editors afterwards, and keep the previous version's installer until the test passes. Do that, and the office layer quietly stops being a topic at all.
The video compares the platforms themselves - and this channel's Nextcloud with OnlyOffice series shows the full editor build when you are ready for it.
Watch Full VideoNo. OnlyOffice and Collabora both integrate with both platforms. This channel happens to build its office on Nextcloud plus OnlyOffice, but the same engine plugs into ownCloud - the two decisions are independent.
Yes. Desktop Office opens files from either platform through the sync clients or WebDAV, exactly as it does from a file server. The browser editor is an addition for quick edits and co-editing, not a replacement forced on anyone.
Technically possible on a platform, practically unwise: two engines writing the same files invites conversion ping-pong and doubles your maintenance. Standardise on one editor per office.