Picking the right distro is a very personal affair. When asking a question relating to which linux distro is best, you're liable to get as many answers as there are different distributions of linux!
Having said that, I second Linux Mint...
It's perhaps the only distro that has everything working right from the get-go without added configuration and is perhaps the best fit from the beginner right through to the power user.
I've tried out many distros starting with SuSe, then moved to Mandrake (later Mandriva), used Gentoo for a long time, Debian, RedHat and then Fedora, back to Gentoo... and then found Mint. One word: awesome.
The one basic element that differs among all the distros is the packaging system. RPM (RedHat package manager), DEB (Debian-based distros: Debian, (K)(X)Ubuntu, Mint), portage (gentoo)... and each one offers varying degrees of user involvement in terms of installation and maintenance.
Some distros require a bit more work to install and configure properly, gentoo (in particular) requires lots of time for proper installation and maintenance (for best performance, the user ought to compile (build) the software from source - which can be quite time consuming and require a little more intimate knowledge of the inner workings of linux for proper implementation), other distros, such as (K)(X)Ubuntu, Fedora, Mint require much less effort to install the OS and little effort to tweak the system for optimal performance. Debian and Slackware are somewhere in the middle of the pack as some hardware requires some code tweaking, with which beginners may not be familiar and which may detract a user from installing everything correctly and efficiently.
Since the vast majority of distros are freely available, however, you ought to download some of the latest releases of the various "flavours" (linux distributions) and find one you're comfortable with by trying out their respective "live CDs".
If you're completely new to linux, I'd once again suggest Linux Mint as a start since it will offer all the power linux has to offer yet is rather painless to install and use. Once you get comfortable, you may like to try out other distributions.
Ah - before I forget - visit
Distrowatch as a source of info on the various distros available. Site offers screenshots, descriptons, direct links, etc. Good place to start.
Hope this helps!
Cheers!