For newbies: Linux Mint
Based on Ubuntu, Mint differs itself by holding back on its release cycle more than Ubuntu proper does. This means when a new release of Ubuntu comes out, Mint is in no hurry to play "catch up," instead opting for using an older code base instead. The idea is that this leaves Mint users with a more stable desktop experience.
Tie this in with Mint's own MintTools, and Mint users find themselves using a Linux distribution that embraces their users with open arms and a newbie friendly environment. I've also come to appreciate their approach to software updates (using a risk numbering system) and the main desktop environment, Cinnamon.
There are some things to be aware of when using Linux Mint, however. First, using Ubuntu PPAswith Mint can lead to issues. Despite Ubuntu and Mint being closely related, they do have some deep core differences that can lead to issues when using some PPAs for software. So be aware of any issues in advance and do a quick search on the Web before using a specific application's Ubuntu PPAs first.
The last thing to be aware of: updating Mint means a fresh installation each time. At this time, there isn't an upgrade tool for installing the latest distro version like with its cousin, Ubuntu.