Office as a whole wipes the floor with LibreOffice. Cleaner interface, generally more stable, especially on Windows, Excel is and remains a powerhouse, etc. Word and PowerPoint are also very solid. Outlook is meh.

If anything, OnlyOffice is incredibly polished. I don't know how they did it but it seems to work better and have a much cleaner UI than LibreOffice even though it's much newer.

OnlyOffice is proprietary software, or freeware if you prefer (they modify the AGPL licence with clauses which are not compliant with the OSD), and by natively supporting the proprietary Microsoft Office document format locks in their users to Microsoft (the company controlling the closed and proprietary format). True free software advocates should avoid it.