About 75% of the people I talk to use Amazon Web Services, 15% of the remaining is Azure, and the rest is split up by Google Compute Engine, Digital Ocean, and Rackspace.
I haven't gotten a chance to compare AWS to Digital Ocean, but there is a huge price difference between the two (AWS being way more expensive).
If you're using AWS, Azure, DO, etc, why did you specifically choose them over a competitor? If there are very differing features, what were those?