I would suggest you do a Google/Yahoo search on this topic, since it usually starts a flame war in places like this. I'm a major Linux geek, but trying to explain why it's better would take pages and pages.
As for the "best" version, that's also a subjective thing. Ubuntu is one of dozens and dozens of different distributions. There are a number of really great "general" distros like Ubuntu, Fedora, Mint, PCLinuxOS, and more. There are a variety of specialty distros that focus on specific areas (security, multimedia, etc).
I recommend that you visit http://www.distrowatch.com which is the "clearinghouse" site for all available distributions. Tons of helpful stuff there.
I will give you a few pluses and minuses that you can research further:
Advantages:
1. Free, as in "freedom" so you can change or customize it anyway you like.
2. Free, as in "free beer." You can download and install pretty much any version of Linux and tons of software for it at zero cost, other than your time and maybe a few blank disks.
3. There isn't anything you can do in Windows that you can't do in a distro of Linux.
4. Incredibly vast support community, including thousands of web sites, forums, etc. Problems can frequently be solved through a visit to your distros community forums or a simple Google search.
5. Choice: if you don't like one distro, try another. Since it costs you nothing, you have nothing to lose. You can try different distros side-by-side on the same system in dual boot or VM. You can install a Linux distro right alongside Windows and boot between them.
Disadvantages:
...I can't think of any.
Read these, too:
http://www.linux.com/learn/resource-center/376-linux-is-everywhere-an-overview-of-the-linux-operating-system
http://www.howtoforge.com/
http://alternatives.rzero.com/