I learned on Slackware in 1994. By 2000 I was using Red Hat. Around 2003 I flirted with Slackware again (as RH/Fedora became more hardware demanding). but bailed for Debian when they dumped Gnome. I dumped Gnome myself about a year later, and Debian in 2009, mainly for Gentoo but now I'm pretty much back on Slackware full time despite intending to only try it "for a few weeks".
When I learned Linux my understanding of and expectations for an OS changed. And change is something I value. The best Linux distro is the one which you have customized and fixed to your liking. Before I left debian I discovered dyne:bolic which was a live cd based on slackware. It had Rasta graphics and was otherwise very similar to (though better engineered than) the debian system I was running. It has a lot to do with why I am back on slackware. Dyne:bolic has been replaced by pure:dyne, which is based on Karmic Koala. There are some minor annoyances with it (though I STRONGLY prefer it to Ubuntu Studio) but really when I sit down and work things out, it shouldn't matter because I know, at this point how I work, and what is right for me, and I know how to do what I should to get it working.
I was listening to a Linux Podcast last night where they were making slackware jokes. I was smiling because they were kind of cute, and because Slackware is not a distribution to use unless you are really willing to take responsiblity for what is on your computer. But there is another irony there. Yes everyone should take responsibility for what is on their computer but people who say you can't do that with Windows are bigots. You can do it with ANYTHING.
The best distro is the distro which best meets your needs, as the best OS is the one which best meets your needs. People who tell you it is Ubuntu or Fedora or Debian are arrogant. I'll vote for Damn Small Linux in a pinch, but Linux is about choice and if you are at all serious then you'll do best with Linux by trying them all.