I have tried many different persuasions, flavors or distributions. This is the list of those that I have tried in no particular order: Knoppix, Suse, Redhat (before Fedora), Slackware, Puppy Linux, Quantian, Scientific, Vector, Mepis, Mint, Arch Linux, KahelOS, Zenwalk, Zenserver, and Ubunutu. I have tried both 32bit and 64bit versions of these and most of these I do not like.
I like most of all SuSe. It is, I think, the easiest to use on a desktop and have most everything work at the start. It is also polished nicely and settings/administration functions are put together nicely in YAST. This is similar to Ubuntu's claim but I have never had everything function out-of-the-box.
I recently started using KahelOS inside VirtualBox. It is a spiffy little distro out of the Phillipines based on ArchLinux. Since it is based on ArchLinux the package manager, pacman, and all the huge repositories are available to use. It uses Gnome as the default desktop environment (DE) and sadly, for now is only available in 32bit version.
Slackware is the oldest continuously updated distribution. It can also be the most different/difficult for someone just cutting their teeth. It is stable and a good way for a newbie wanting to learn. The user is forced, more than other distros, to dig in and understand the nuts and bolts of how things work in GNU/Linux. That is a good thing. I learned a lot by using it.
Knoppix was another very useful distro. As a full linux distro on a CD without installation, it was a novelty when it first hit the market but is still nice to have on hand to repair, hack a system or have on hand to demo it to someone new to GNU/Linux. With the last few releases Knoppix has gotten big enough that it is downloadable as a DVD. You can get stripped down versions of it onto a CD but it is not the same. I am not sure if that is due to KDE getting bigger, wanting more packages to be included, or why.
I have tried various spin offs that are in the -buntu world. They are just not for me. To me they seem almost contrite and forced. There are also a lot of annoying users. That said, the forums and helps that have been put together are a great help to the rest of us too.