There has always been an argument between distro users of linux ,which distro is the best.Let me say one thing different distros are meant for different purposes.For example ubuntu is suited for home and office use ,while backtrack is a must for penetration testing.Nimblex suited for ones who are very specific of what they want in their computer.So let me come to the point i am pointing out the most popular ten linux distributions which are : Debian, Slackware, Fedora, Mandriva, Suse, Ubuntu, Knoppix.You need to note that there are about 350 distributions of linux.I wont say that they are not good ,but i may list out the ones which are mostly preffered .The choice of os depends on people .It cannot be confined to some distributions.Here is a brief introduction:

Debian : It is one of the oldest linux distributions.It was first developed by Ian Murdock.It supports about  15,000 packages on 11 architectures.Debian is known for its strong adherence to the Unix and free software philosophies, its stability and its huge community.Due to the high stability and quality it is mainly used in servers which need to be very stable.Official website: http://www.debian.org

Slackware :

It was founded in 1992 by Patrick Volkerding, and it is  oldest surviving GNU/Linux distribution. It is a very minimal distribution with high stability .It has a very minimal package management and installers are text based.It is suited for admins who are very eager to understand the working of linux and for novice who are very eager.It is in no way an eye candy and what ever one learn from it is available for every other distros.Rather than using distribution specific configurations one needs to edit configuration files manually.Official website: http://www.slackware.com

Fedora:

One of the best known Linux company in the world is Red Hat, founded in 1995 by Bob Young and Marc Ewing.It was later converted to Fedora Core.It uses rpm installation packages.It has installers like yum etc.It is a candy in every facet .It is a general purpose distribution.Due to close resemblance to redhat it is very popular to companies too.It has a very excellent graphical interface.Official website: http://fedora.redhat.com

Mandriva:

It was originally called Mandrake and it was created by Gael Duval in 1998.It is a great option for novice with a powerful graphical installer.It is based on redhat and it uses rpm packages.In this gnome has been used earlier which have been replaced by KDE.It is highly up to date and therefore has a lot of users.Official website: http://www.mandriva.com

Ubuntu

Ubuntu was created by Mark Shuttleworth and is distributed by his company Canonical Ltd.It was first released in 2004 and has taken over the market over these years.It is not good as mandriva or fedora in its appearance.It has become so popular as it offers free ubuntu cds including shipping charges.Every new version is much better than the previous versions and it is its quality.Official website: http://www.ubuntu.com

Suse

Suse is one of the best choices for a desktop install.It is well known for its installer and configuration tool named  YaST.It is a good os from the boot to to its appearance.In 2003 it was taken by novell and it began distributing .iso for free all over the web.It is based on KDE environment.Official website: http://www.suse.com , http://www.opensuse.org

Knoppix:

Klaus Knopper,was the man behind the  Knoppix ,which is a live-CD distribution which can run from a cd without the need to install on a harddisk.It has a high compression efficiency and a much better hardware recognition much better than other distributions.The CD can be used as a recovery or administration tool or even used for a live demonstration session.This is based on unstable debian edition and its updates are quite uptodate.Official website: http://www.knoppix.com