According to ntldstats.com, the new gTLD .XYZ has passed .Mobi in the number of registered domain names.
The .Mobi registry which went live on September 26, 2006 according to RegistrarStats.com has 791,396 domains under registration having lost over 1/3 of the registrations it had at its peak in 2014.
According to ntldstats.com (which does not track legacy TLD’s), .XYZ has almost 795,000 registrations.
Registrarstats.com shows that .Mobi had around 1.2 million domain name registrations as of January 2014 and therefore has lost more 400,000 registrations since then or over 33% since.
.XYZ has the most number of domain registrations for any new gTLD.