PC is more powerful (market share)
IMO, Mac is better. I'm a power user, and I can have everything on my Mac:
* easy to use
* Built on UNIX and you can use UNIX programs
* easy to install Windows on
* no viruses (yes, its true)
* extremely secure (just don't forget your password :p )
* good for new computer users and power users alike
* Software and hardware is made by the same people - so it runs better
* you almost never have to install drivers
* and many more things which I can't think of right now