I've used slackware, redhat, freebsd, openbsd, gentoo, suse, debian, xandros, mepis, knoppix, and mandrake. I've used linux pretty much exclusively since 1995.
This question of which linux is "best" comes up constantly in the linux forums. As is already apparent in this thread, there is no "best" distribution; everyone has a favorite and many people will insist that their favorite is the "best".
My answer to this question is always the same: decide for yourself. Each linux distribution is basically the same underneath, each one is flawed in it's own special way, and each one has advantages over the others. Just start here:
http://distrowatch.com/dwres.php?resource=major
Read each blurb, pick the one that most sounds like what you are looking for.
Personally, I use mostly Debian with SuSE on my desktop at work. My wife uses Xandros (hey, that's TWO females using linux). At work I do a lot of work on redhat servers, and I think many companies use redhat (though this is changing). But what I use is not necessarily what someone else would want to use.
Most people would want a Mac, right? I'm still scrimping...
-kev