One way of looking at it is who has final say what ends up in the documents. That seems to be what you're discussing.
In the W3C, that's the Director, Tim Berners-Lee. Except, as pointed out elsewhere in this thread, he has delegated all his decision-making powers to W3C staff. So ultimately it is the W3C CEO and the folks he hires.
In the WHATWG, that's the browser vendors (i.e., the WHATWG Steering Group). I find the WHATWG model to make more sense, as I think what ends up in specs should match what the implementers plan to do; that makes for a more useful spec ecosystem for everyone. When you diverge too far from that model, you get circa-20004 W3C, i.e. XHTML 2, XForms, XEvents, etc.
A different way of looking at it is who contributes to the discussion and development of features. In the W3C, that's paying member companies (https://www.w3.org/Consortium/fees, $2.25-$77k/year in the US). Although anyone can comment on GitHub, to contribute ideas that get incorporated into the specification, you need to be a W3C member, for IPR reasons. (Or invited expert, but that has its own problems; see https://medium.com/@tobie/w3c-doesnt-help-its-invited-expert...) In the WHATWG, anyone can contribute; the IPR concerns are taken care of by signing an agreement, somewhat like an open-source project CLA, but that agreement does not require paying membership fees.
Overall, I think the WHATWG structure, of being open to input from all (instead of pay-to-play), with the spec tracking what browsers intend to implement (instead of tracking what W3C staff deems good), is a pretty great model for standardization.