Don't listen to anybody telling you to use anything but Ubuntu. If you're a first-time Linux user, you're going to have a bunch of stupid little problems which are already answered by other people on the internet. When you use Google to discover how to solve these problems, they will be answered for Ubuntu. Once you're experienced, it is easy to translate the sequence of steps into whatever distro you are using, but you need to learn the basics first. Don't think that what you start off with will be the same as what you end up with; you're going to reinstall your OS at least once. If you hate Ubuntu's interface (which you should), I would recommend Kubuntu (
http://www.kubuntu.org/). It is the same as Ubuntu in every way except the desktop manager is KDE instead of Unity.
I would advise staying away from Gentoo, Arch Linux, and Slackware. They're horrendously difficult to manage. As an experienced Linux user, I find the extra options they add to be completely fucking pointless and a total waste of time (good luck going on vacation and trying to emerge without getting a headache). I would be pretty amazed if a new Linux user could even get any of them installed properly. After that, I would ask why the hell they didn't just install Ubuntu.
Personally, I use OpenSUSE because it has a stable base which is easy to extend. The package management system, RPM, is one of the most robust systems for deployment I have ever used -- it works in exactly the way I want it to. This means package management through zypper (or YaST) is fantastic.