Hah the question of the ages... What do you plan on using it for / what kind of computer user are you?
HI if you want user friendly then windows, but if you want good secure, and virus free, then use Linux platform OS .
Excellent. Another stupid thread where I can post a witty photo of one of my old computers running an OS that nobody uses any more. The "best" operating system is GEM/Atari TOS.