If you have to ask, choose Ubuntu. Ubuntu is far and away the most accessible to Linux newbies. The Xubuntu and Kubuntu variants are actually better, though. However, if you're wanting to move beyond Ubuntu, there are many options. Arch, Slackware and Gentoo are three common enthusiast destinations. Fedora, OpenSUSE and Debian itself are common moderately-involved choices. Zealotry aside, there is no one be-all end-all distribution, so it may be wise to try a few before settling on one. DistroWatch may also be useful.
there is no one be-all end-all distribution,
This is why I included what I would be using it for. I tried Ubuntu and didn't like it, it felt much too bloated to me and Unity is really terrible in my opinion.
Arch, Slackware and Gentoo are three common enthusiast destinations. Fedora, OpenSUSE and Debian itself are common moderately-involved choices.
Thanks for these recommendations, I'll take a look at them on DistroWatch.
Even if you do not choose to use arch, please take a look at the wiki. I found it to be one of the better linux wikis out there.
The Xubuntu and Kubuntu variants, I also recommend. They don't have the hideous and nigh-unusable "Unity" desktop interface that Ubuntu introduced as a default a few years later.