I've been using Google Drive, Dropbox and One Drive concurrently for a long time. I have made three well spaced separate attempts to use and enjoy iCloud. I really would rather use just two. Google and iCloud. But after the MobileMe Debacle involving a small number (my luck) of users having more problems than I care to spend the time listing here I've avoided iCloud for the present. Notice I haven't condemned it and quit, just giving Apple the year or two it'll take if they choose to focus on it. They can be fast or slow, cloud services baffle Apple so it'll be awhile.
The good news is that Apple did take ownership of my MobileMe and iCloud cases and helped to retrieve some of my data after two months. Kind of slow but I always give credit for the help. That they didn't get it all is just the risk one takes with any such issue.