Well... I'm an Arch Linux user - I have Windows XP, Arch, FreeBSD and OpenSolaris installed, but I only use Windows XP and Arch, the BSD and Solaris are there just for learning purposes.
I have tried... too many distributions before, such as SUSE, RedHat (before Fedora was born), Fedora, Mandrake/Mandriva, Linspire (when it was called Lindows), Xandros, Mepis, Debian, Slackware, Ubuntu, Yoper (very interesting one) and a few more.
The most newbie friendly for someone who doesn't want to tinker with it but to use it, Mandriva seems to be the one. Ubuntu/Mint wasn't bad either, nor was Fedora, but if you want to get it installed and working fast, get Mandriva or Mint (both come with most codecs preinstalled, Mandriva should have some proprietary drivers included as well).
If you want one with long term support, install CentOS.