Answer by Jimmy Wales:
I'm answering first with reference to long haul flights.
Sometimes I do. People often pay for my travel when I am coming to give a speech for them, and that's usually business class but sometimes first class. And because I fly quite a lot, I sometimes get upgraded from business to first.
I pretty much never fly first if I'm paying for it myself. Business class is often worth it because I can sleep and be more productive and also spend less time away from home (no need to schedule in extra time to recover from flying without much sleep). But the upgrade from business to first is generally not worth it.
I once paid to fly in first on a trip from London to Mexico because for unknown reasons it was actually cheaper than business.
Finally, whenever I talk about flights, I like to emphasize that the Wikimedia Foundation has only paid for 1 flight by me in… I guess it's been nearly a decade. When I'm doing work for the Foundation (such as attending board meetings) I insist on paying for my own flights.