Debian: It's stated goal is "Free Software", as per the goals of the GNU project (http://www.gnu.org). So its correct name is Debian GNU/Linux. Extremely powerful, its package management system (apt-get, dselect) and other features make it easy for you to upgrade your system. Debian's stated belief in free software also means that you won't get any commercial software in Debian, whereas the commercial versions (full, multiple CD packs) of other distributions include a lot of commercial software.

Conclusion

Now you can select Linux according to your requirement. This is the beauty of Linux. There are so many various kinds available that you can be sure to find one to suit your needs.

For a far more detailed article, try the Linux distribution howto by Eric S Raymond at http://www.ibiblio.org/pub/Linux/docs/HOWTO/Distribution-HOWTO

(Yes, he's the same "ESR" who wrote the fetchmail POP client and maintains the Jargon file. Take a look at http://www.tuxedo.org/~esr for more).