Which Linux distro for programming environment?

I'm on PCs so I'm far removed from UNIX or the command line environment. However I see on a lot of job postings on the web that people familiar with Linux earn a few extra points plus the fact that I want to learn it for better interacting with servers. So, I'm really want to try to do more of my basic computing and coding in Linux just to get familiar with the environment and learn more. So what's the best distro to use? I know Ubuntu is probably the most popular but I hear people say that you'll end up learning Ubuntu and not Linux. I hear things like “If you learn a Linux distro you learn that distro, if you learn Gentoo you learn Linux”. And that Gentoo is harder to use. So I'm drawn to Gentoo because it sounds like I'll get more of the core. However I'm worried I'll end up spend to much time trying to just get the thing running, that I won't learn any of the surface level stuff (which is better in the long run if I wanted to be serious about Linux, but I don't think I need to be that serious) Finally there's Debian which seems like a nice mesh of easy to use but still gets to the core of Linux. The only thing I've done with Linux is installed it back in college so I could play Kbounce :). I'm ok with the command line after going through the course here and want to use it more.

any ideas or thoughts? I'll install it with Virtualbox on either my i7 laptop or AMD Phenom II X4 desktop.

thanks.