It is dependent on your usage scenario or requirements.
They all offer cloud folder synchronization service. In general, they have similar features and client software. For consumers, the difference is small. It is a matter of preference.
For businesses, the difference is slightly bigger: OneDrive for business is tightly integrated with Office 365. If most of your files are MS Office files, then OneDrive has a clear advantage. For businesses that heavily use Google Docs, then Google Drive has a clear advantage. Dropbox seems to be in a weaker position, but it is more popular in the consumer service market, thus a lot of business users might be more familiar with Dropbox.