I have been paid user of Dropbox for now 4+ years. The reason I have stuck with it because "It works! plain and simple." I have tried other storage services like Google, iCloud and Box. But none match the simplicity, consistency, invisibility, cross-platform, seamless features of Dropbox. Google is untrustworthy because you never know when they discontinue any service. They have no concept of customer service. They might well be running by robots. I experienced Box at work, forced by the work IT group. IT wasn't very willing to hand out Box accounts unless you can justify business use case , people who used it didn't like it. Box interface was always in your way if you wanted to do anything stored in Box, few extra clicks to do anything. Most people who needed to collaborate used free Dropbox to get around all restrictions. iCloud is okay but only seems to work with Apple ecosystem. I still can't figure out how to access files in iCloud from my Mac and iPhone. Works great for photos and contacts but not so much for files. While Dropbox has released new features, I have never bothered with any.
IMO, Dropbox need to continue focusing their service seamless. There only mistake was to not go after business/enterprise earlier. They could have killed Box easily. While Box was hiring consultants and Enterprise sales people to pitch to IT groups (top down) Dropbox had the mindshare of employees (bottoms up). They were Dropbox champions, just Dropbox failed to leverage that in enterprise.