CentOS is a great server distro for a tech-saavy Linux beginner such as yourself. I say this for two reasons: first because it is what your workplace requires, and second because it is extremely well-documented (the CentOS wiki is outstanding, plus you can use just about any Red Hat Enterprise Linux materials as well, such as Michael Jang's "RHCE Linux Study Guide").
That's assuming you'll be using CentOS as a server to practice your admin skills. If on the other hand you are looking for a general-purpose desktop/laptop distristribution to "get your feet wet" with web surfing, multimedia, games, etc., then there's certainly nothing wrong with CentOS, however you might also consider Fedora, which has the same "guts" as RHEL/CentOS, but has a faster development pace, providing the latest kernel, hardware drivers, applications, etc. every 6 months.
The Debian/Ubuntu/Mint family is also very popular, but because it uses a different package management system (DEB instead of RPM), you'd have a slight learning curve switching to CentOS in the future.
You'll probably also get a few votes for Slackware here on these forums.