And now Ubuntu has passed Red Hat in the # of servers metric because devs like me choose their Linux server OS based on familiarity with the Ubuntu desktop OS.
On the other hand, Red Hat's revenue is steadily growing[1] and there are very few RHEL desktop users. Fedora is probably also less popular than Ubuntu and its derivatives.
Interesting question. Some data points that I could find.
Canonical: 2009: ~30M, 2013: 65.7M, 2016: 103.3M
Red Hat: 2013: ~1.4B, 2015: ~1.8B, 2016: ~2.1B, 2017: 2.4B
Consequently: Canonical 2013-2016: ~1.57x, Red Hat 2013-2016: 1.71x.
So, their revenue seems to be increasing at a slower rate and Red Hat's revenue is almost twentyfold that of Canonical. Moreover, Red Hat is operating on a quite large profit, while Canonical is on a loss.