Personally, I prefer Dropbox. I found problems with One Drive. Google Drive client was always hit and miss and I could not rely on it. iCloud is not cross platform (afaik). Dropbox has worked where ever I needed it.
Dropbox is more expensive but I prefer to have my files in Dropbox (as a separation of concerns) rather than have a single tech company control every aspect of my life.
My experience with the 'average Joe' is that Dropbox is easy and it works. Yes, they might save a couple dollars switching to OneDrive but Dropbox still offer a good product. Will Dropbox survive long term? I certainly hope so. I have no affiliation, aside from being a customer.