In terms of LiveCD's, I'm a SLAX lover because I have a fetish for eye candy.
On the desktop, I use LinuxMint mainly because I like their view and direction, even if it isn't "pure" Linux. I think believing in a distro's view is important when choosing one.
Another is Fedora in general mainly because they are complete bleeding edge but also extremely stable.
And finally, Gentoo. I love the portage tree and getting that small (or sometimes huge) performance increase from compiling everything is great. They're also constantly pushing new technology.
I'm a huge "distrophile". I love to try new and obscure distros and rarely do I find one that I dislike. But major ones that I do dislike include OpenSUSE, Freespire, and Foresight.