Best is a funny word to use because best is subjective. Best doesn't even specify in which way the OS needs to be 'best'. I guess...
For the wealth of applications, Windows.
For a frankly limiting level of ease of use, OSX.
For a confusing but potentially rewarding experience, Linux. But not Ubuntu as
You must login or register to view this content.. Fedora, Debian, Mint and some others are all better options. Of these Mint is the most 'user-friendly'.
I use Windows 8 but solely due to the still lacking gaming support for Linux. That appears to be changing though so I'll be switching it up soon enough.