I guess it all depends on what you want to use the machine for. If I was going to run a server, I would typically choose FreeBSD (most secure out of the box), or Redhat (largest community, so makes sense it would get the fastest updates). For programming needs, I choose Debian especially since the apt-get program will give you a boner. For a personal computer, I typically use Mandrake (just like it, that's all), or Debian. For the fun of it, I also like playing with Gentoo.
What, no mention of
OpenBSD for most secure out of the box? Heck, its /usr/bin/perl is even 5.8.0 (as of 3.3). I use this exclusively at home - the only beef I have is the poor support (which I last tried in 3.2) for Java.
