I now have Gentoo on my Desktop and keep Debian on my server.

Remember: One distro isn't always better than another - it's usually just different.

I still use Debian because they keep out untested packages.
I use Gentoo because they'll throw anything in.

I'd use Slackware if I want Vanilla and the .tar.gz method.

My personal opinion is to look at the following when considering a distro:-

- Social Contract
- Packaging System
- Packaging `Contract`; what packages are allowed in

I switch to Gentoo from Debian because of the KDE3 / XFree4.2 issue - it highlighted for me the strengths of Debian and time for a change to something more approprite.

That's pretty much it.