Let's cut to the chase. Android[1] is the most popular of all Linux distributions. Period. End of statement. But that's not the entire story.
Still it must be said, according to StatCounter[2], Android is the most popular of all operating systems[3]. By a score of 39.49 percent to 36.63 percent, Android beats out Windows for global personal device supremacy. Sorry Windows, you had a nice run, but between your smartphone failures and the PC decline, your day is done.
But, setting Android aside, what's the most popular Linux? It's impossible to work that out. The website-based analysis tools, such as those used by StatCounter, NetMarketShare[4], and the Federal government's Digital Analytics Program (DAP)[5], can't tell the difference between Fedora[6], openSUSE[7], and Ubuntu[8].
DAP does give one insightful measurement the others sites don't give us. While not nearly as popular as Android, Chrome OS is more popular than all the other Linux-based desktops combined[9] by a score, in April 2018, of 1.3 percent to 0.6 percent of end users.
As for what most people think of as "Linux distros," the best data we have comes from the DistroWatch's Page Hit ranking[10]. DistroWatch[11] is the most comprehensive desktop Linux user data and news site.
But you can't make too much of their numbers. As the DistroWatch site managers themselves say, "The DistroWatch Page Hit Ranking statistics are a light-hearted way of measuring the popularity of Linux distributions and other free operating systems among the visitors of this website. They correlate neither to usage nor to quality and should not be used to