I found this article quite helpful to the beginners or those looking for linux distros/distribution for a desktop machine;
“Which Linux Distros I should Choose for my desktop machine”
This depends on personal taste, however if you are a beginner looking for a desktop machine you can go for ubantu or SUSE or Fedora Core, on my personal taste Suse, Foresight Linux and Fedora Core are nicer to use while Ubantu is more like a real linux system that need some advance knowledge. Ubantu and Suse both have the larger userbase. Most of the problem regarding any working solutions are usually covered by their forums such as laptop installation, adjusting monitor resolution etc. However if you are more advanced you may consider to go for Debian Network Install CD, it takes a little more work to get it going on such as apt-get install gnome to install a user interface.
If you want to take your linux experience to try out more bleeding-edge software, you will difinitely try to taste Gentoo though it is hard getting it going but you shall learn a lot about linux in process.
If you need a specific package management system, be aware that
Suse and fedora core use RPMs, Ubuntu and Debian use DEBs and
Gentoo will use Ebuilds with portage.