I have accounts with all 4 services (iCloud, Google Drive, OneDrive and Dropbox). Am now using iCloud primarily, but also Google Drive for some of my Google Sheets requirements.
I also had the same experiences as you when it comes to OneDrive. It is amazing to me that so many people in the Microsoft ecosystem thinks that crashes are an expected occurrence. Drove me crazy.
Migrating files from OneDrive to iCloud was no problem. Just copy & paste thru Finder. Keeping files on OneDrive just as a backup of sorts.
Some people in this thread have commented on iCloud syncing issues, i.e. delays. I have never experienced this. Have almost 500Gb is business files (no photos, music or movies) and iCloud is by far the fastest of any of the cloud services. Only difference is Dropbox has LAN sync which does speed it up between computers on a local network. Otherwise their regular sync is not as fast as iCloud.
Just my 2 cents.