I've tried quite a few: Redhat, Suse, Corel (lol), Slackware, Mandrake, Gentoo, Ubuntu, Debian, Smoothwall, IPCop.
I only voted for Gentoo, Ubuntu & Debian tho as those are the latest ones I've tried that have actually been usefull. Slackware was ok, but that was a few years ago. Think my first linux install was in 1998 or something.
The best imo are:
Ubuntu - for ease of use (aswell as being very customisable, using deb's)
Gentoo - amazing for someone who wants to learn or has knowledge and wants a totally custom system, even down to compiling. Stage1 is excellent for learning. Also amazing distro for firewalls/IDS etc.
Last time I tried Suse I hated it as it tried to be windows and tried to do everything itself, including falling over itself several times. Mandrake was ok, but stupidly slow and bloated until you tweaked the services etc.
I think redhat was ok, but Suse,Redhat+Mandrake all fall into trying to be windows and result in falling over themselves aswell as being bloated
