I do thunk that most mainstream users would probably be better off with OS X though. It looks sleeker and feels simpler, which is what most people would prefer.
In my opinion? Then I guess I would pick Windows 7. I have actually not tested any of the listed operating system. I only tried Windows 95, 2000, XP, Vista (using now) and probably some earlier version of it. I believe mac is more powerful than Windows. But as said, many games and programs are impossible to run at mac. The linux ubuntu one is definately a cool operating system but I'm pretty sure it's just cool at the outside.
I'm having a feeling mac is better for experienced computer users though. I have to test it sometime.