Literature and Latte recommends dropbox as it is the only cloud syncing solution that doesn’t foul up the project files. (As per this blog post.) If you chose to use this route, just make sure to close the file, and wait for it to sync before opening it on another device. Most of the issues you see with dropbox are because people fail to follow these very simple guidelines.
Alternatively, you can manually copying the file to and from a flash storage device, but that has hazards of its own.
Apple sync services are not as good as dropbox ones in my experience as well.
I saw scrivener project files are macos packages, Dropbox plays nice with those files and it syncs them one element at a time, so I guess it would be difficult to get a mess.