[silas]

CentOS, Fedora and RHEL use Python for most of the system tools and as such integrating or contribute to those projects will be easier if you know Python.

That said the recent/popular systems automation and conifguration tools (Puppet, Chef, etc..) are predominantly in Ruby, so that is a good choice as well.

I prefer Python, but as spooneybarger said, if you end up using the systems version of the interpreter with CentOS/RHEL you're going to need to learn the differences between versions. Luckly EL 6 is coming out soon and you'll get a fairly up-to-date version.