There's a difference between the best distro and the best distro for a new user.
The best distro for a new user would be LinuxMint. I absolutely loved it! Need to install...go to MintInstall. Since it's based on Ubuntu, you can use apt-get in the terminal and ask for help on the awesome ubuntu forums (though the LinuxMint forums are also pretty good). The out of the box functionality of LinuxMint is unmatched.
If you have a basic idea of using Linux, I'd suggest Fedora. It's what I'm using now, though I had some issues with drivers, especially for sound. If you're used to Ubuntu or other .deb package distros, it might take some time to get used to .rpm packages, but it's as simple as typing yum install firefox
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Fedora is what Linus Trovalds actually uses. For the uninitiated, that's the author of the linux kernel.
Fedora's really beautiful though and the community is friendly and helpful. I'll be trying out Debian on my desktop next month and I'll post a review once I get around to it.
If you have an old computer though, nothing, and i mean NOTHING can beat Xubuntu. I use it on a 9 year old desktop... 800 Mhz, 256MB RAM, 10GB HDD and 64MB Geforce 2 card, It runs like a dream!! That is for Intel processors though. If you have a PowerPC, you have little choice but Fedora as it's one of the few distros that has a special version for the PPC.
As you can see, there's absolutely no limit to choice when it comes to distros. If you want a really gorgeous desktop, use a KDE based distro (Opensuse, Mandirva, Kubuntu etc). For out of the box functionality and ease of use, there's LinuxMint and Ubuntu. For a more traditional distro, you can try Fedora, Debian, Knoppix or Mandirva (again). If you REALLY know what you're doing and want some really customizable, use Gentoo and it's crazy Portage BSD. Make sure you have a good internet connection with no download limit.
Out of all of em, I'd go with LinuxMint (which is a better version of Ubuntu, with the same release cycle), Fedora or Mandirva. The rest are all good, but I personally wouldn't use them