I'm surprised engaget included Amazon in their comparison as Amazon lacks filesystem integration (on MacOS and Linux; dunno about Windows) which doesn't really make them competitors for Dropbox, Box, Google Drive or iCloud.

Dropbox seems to have the best integration despite their underhanded use of Accessibility capabilities.

Our company has tried to use Google Drive, but found too often the client would claim that the sync was up-to-date while in fact it had simply stopped synching. We now have a Frankenstein system of google docs for text, GD for a library of PDF literature (for historical reasons), and DB pdfs, powerpoint and excel, and code. Sucky.

We used Box at a previous company. Meh. It seems to be aimed at F500 companies.

Oh and I continue to get a stream of confidential documents from another previous employer who standardized on Google, despite my efforts to stop it. Lucky for them I'm a nice guy since I'm no longer covered by NDA ;-).