As I am working with both, mac and windows devices, the easiest method to sync my files is with OneDrive. This method runs smoothly and I don’t plan to change it in the future, as I use Azure as my primary cloud-service for literally everything. Now with the mobile app on the way it would be really great, if I could sync my existing knowledge-bases from OneDrive to my mobile-phone. This would help me and hopefully other users a great bit with remote working on our files.
On iOS, OneDrive needs to allow apps to access its files via the File Provider API before Obsidian can access a vault there. So, make sure you submit a FR on that request too.
Android:
It doesn’t work with the native Onedrive app.
I solved it with the Onesync app:
This syncs any folder, in my case the Vault folder, directly to a folder in Android. This folder can then be specified as the Vault folder in obsidian mobile. Works great in both directions.