But first a definition, when I say WiFi hotspot I mean in the traditional sense, that is predominantly serving the hospitality industry with the network controlled by hotspot management software (i.e. a basic WiFi router with open access does not qualify). Secondly, when I say operator I mean the company in question largely, but not necessarily exclusively, owns and operates the access points that comprise their network. Lastly, saying that these operators are the most prominent is a bit vague, and so as qualifying criteria I add number of access points being operated by any company as being in the hundreds.
Here is my listing of the my perception of the top four in alpabetical order: