I haven't made much use of cloud services yet (other than testing/playing around), but I'm sure I'll fit them into my "workflow" at some point.
With that said, I have the 5gb available with Google Drive and a total of 50GB (two accounts, 25GB each) with Skydrive: my two accounts were upgraded free to 25GB as I was an existing user at the time.
So, I'll probably use the 5GB Google account for small files like documents etc, my "main" MS account for larger ( but frequently accessed files), and my secondary MS account for general backups that I'd rarely need to access.
That's what I'm thinking, anyway. All that is subject to change once I get some real world use out of them...