Definitely Slackware in my computer. I've tried Fedora, Redhat, Gentoo, and Debian and Slackware is by far and away my favorite. Much faster than the others and great compatibility for beginners...
And they're all also big files, so you wanna have quite a strict path to follow.
Xandros has a free version that isn't too big (i think it was just less than 500MB), and is supposed to be great for beginners, so you might want to try that out.
