Many times when people are looking to switch over or try Linux, they question which version or distribution is the best. There are quite a few different choices so it seems obvious that one must be the best. The reality is that there is not really a best version of Linux. There are different versions that meet different purposes.
Before you can pick what you think is best, you need to understand some of the philosophies behind Linux. Some people want to only use free software. This does not mean software that does not cost money, but software that is entirely free. Just because a piece of software is on a Linux distribution does not mean it's entirely free. For those wanting this distributions like Fedora or GnuSense would be best because they try to stick by the philosophies of free software as best as possible.
Others do not care so much for this. At this point it's based on what features you get. Ubuntu is one of the most popular distribution because it's so user friendly. Many in the last few years have been introduced to Linux through this distribution. The advantage that Ubuntu has is that it has a large user base so most bugs and issues are taken care of.
There is a version of Ubuntu called Linux Mint that is much like Ubuntu except that it has a different look and feel as well as comes with proprietary software like flash, java, music, and dvd playback. It also still has access to the very large body of software that Ubuntu and Debian support.
Regardless of the reasons you enjoy the distribution that you choose, there really is no best. Since it's Linux, try them all and see what you like the best.