Well first off DO NOT direct install Linux on a Mac unless your geek skills are of a college level computer graduate as it will seriously mess up a Mac.
You can run whatever distro fancies you in VirtualBox.
Scroll down on this page on the bottom right is basically a scorecard based upon hits
http://distrowatch.com/
Linux Mint has (ever since Shuttleworth went bonkers with Unity in Ubuntu) has been the overall favorite Linux geeks distro of choice and the choice of newbies as well due to it's complete and effortless installation.
http://linuxmint.com/
There are slight desktop differences for Linux Mint, but that's what a lot of Linux geeks like is choice, which they lost when Unity came along and issues with Gnome 3.
All I can say is try out as many distro's as your boot drive has space and settle on one that has the most software and options and things you like about it.
There are hundreds of distro's some with their own software, some tailored for particular fields or interests.
Just be careful visting Linux websites and registering and asking stupid newbie questions, your likely to get your Linux VM pwned by someone for kicks. 😉
But VM's are usually safe, you just revert to a earlier snapshot. 🙂
Want to try Linux?, read this