I use Dropbox for my cloud storage, as it is platform agnostic. Apple's solution does not extend to Android (yet), although it does support Windows.
Dropbox has not been without problems. A Google search will reveal some interesting stories and much finger-pointing for everything from "leaked" tax returns, loan applications, and compromised passwords, to deleted files. Choosing unique, secure passwords and enabling two-factor authentication are a must in today's world. As well, file-level encryption of sensitive documents would be appropriate for anything sensitive, like a tax return.
I'm intrigued with Apple's Photos sync, much more so than Google's, due to the privacy and ability to store original files how I choose. For that, I may upgrade my iCloud storage space.