There are several factors that affect the choice of flavor of Linux you choose. However, let us first consider what you’ll be using it for. If it's a home desktop or office type workstation, it is most favorable to consider Mandriva, SUSE, Linspire, MEPIS, Xandros, Core, and Ubuntu.
If you are using a small to medium business server, then you can try Debian, CentOS, SUSE Linux Enterprise Server, Fedora Core, Turbo Linux, Vine Linux, LASER5 Linux, Kondara MNU/Linux, or RedHat Enterprise Linux. These statistical distributions can host online pages and databases for an intranet, handle e-mail, and operate and manage a network and printers. The most popular distribution today for businesses is, of course, Debian GNU/Linux.
If you have a few older PCs, you could change them into thin Linux platforms where they can be utilized for a router or firewall. Slackware happens to be the oldest distribution of Linux, while Plamo Linux based on Slackware requires a considerable level of knowledge for operation.