Whenever somebody uses the phrase "The best Linux distribution" It's time to get out the old asbestos underwear, cause there's going to be a flame war. It's almost as bad as the old and pointless KDE vs GNOME argument, and no more likely to be settled in our lifetime.

That being said, I have to point out that Slackware doesn't suck as much as you think. I learned Linux on Slackware 3.3, and I liked it. No GTK out of the box, thread-dangerous Xlib, an installer that's really just a front end for gunzip, and no useful help on setting up an X server. (Sign me up for the "Hardcore masochist" category, I guess). As for security, old slackware won't get you 0wnz3r3d nearly as fast as Red Hat of the same vintage.