in my experience Debian derivatives have always had the most rich package set out there. anyway corporates do not need any package but well known packages.
US is Red Hat, Europe is as split between Red Hat and SLES, but even here people is asking for Red Hat certification not SLES...
more dynamic versions of the distros are fedora and opensuse. they are just ahead of their respective corporate versions and stay more uptodate but less supported (no paid support). so learning fedora is learning red hat. same fits with opensuse <- >SLES.
just mind that when a new tech is introduced in fedora/opensuse, corporates can still lag and use previous stuff. Well, this is actually more true for red hat/fedora than for opensuse/SLES, in fact the latter has aligned their releases (more or less).
debian is a different world: no corporate support behind it, so no gain in corporate envs. Ubuntu is a derivative which tries to provide corporate support, but, honestly, it is not their stronger point at all.