Joplin Cloud will at be faster and more optimised regarding synchronisation, that's for one. Also, if you ever need to receive one-to-one support, you will likely have a much higher change for that with Joplin Cloud than something like Dropbox or OneDrive (i.e. good luck finding a direct contact with someone at Microsoft!).
Personally ,I would always use a "separate cloud drive for Joplin". The idea is, when the same drive is used for many different purposes (with many wrote operations) the chances of another application accidentally deleting or changing Joplin files (even if protected) does exist. With so many free nextcloud offers I would keep my Drob or ONedrive and use it as before.