When Google Drive and iCloud and One Drive all cropped up, copying the same service with the addition of deeper integration into different devices and software, I was worried Dropbox would be unable to compete. But they've hung in there, and I remain a happy customer.
Out of curiousity, what does Dropbox do for you that they don't? Have you stayed because of price, service, features, laziness to switch? :) I personally don't have many storage needs so I just email myself important files, back up some things to USB, and sometimes will add things to Google Drive
You could share a file with your colleagues by simply emailing a URL to the file. No other service was as straightforward at the time.
When that feature was later removed, I stopped using Dropbox.