I use Gentoo. I used to use Fedora Core and used it for almost a year. Then I discovered Gentoo and I fell in love. It was the fastest distro I had ever seen, given that you cutomized the kernel and every aspect of the system. Plus, it is difficult to install and I'm always up to the challenge.
However, wha I really love about Gentoo is Portage/Emerge/Ebuild. Portage is a great tool. You can dl all the programs you need and build them from source with no problems. It has automatic dependency resolver where as Yum doesn't.