Of the two, I'd go Slackware.
I've tried Debian a time or three, and had nothing but bad experiences with dselect. Plus they don't seem to have terribly up to date packages sometimes, even in the unstable tree (older versions of kde, etc.). I will give it credit for this - I was able to get it running on an old laptop with nothing but a floppy drive and NIC. But I couldn't really see myself doing anything serious with it.
Slackware is nice - an extremely minimal system, do pretty much everything yourself. I was running it on my server last year up until spring break, and was fairly pleased. It's my second choice for a distro (Gentoo being the first).
Its package system, however, is abysmal. Great for installing a base system, not so great for updates IMHO. I usually just install some core stuff, and any more desktop-ish software, or other stuff I'll be wanting to update, I download sources and build myself. The distro can give the user an incredible amount of control, but that comes at a price.
Now, where's my squire? This plate armour is rusty. |