Key points here for PCs:
Run the vast majority of software available today.
Will run on vast majority of hardware available today.
Upgrades can be difficult and problems often arise (that's why this forum exists).
Most popular OS in the world.
More suseptable to viruses etc ( because there are more for windows than Mac)
Most configurable OS.
Arguabley less stable than Mac.
Cheaper and more variety in hardware.
Personally I'm a Mac but I run 'Best of Both Worlds' known to most as Boot Camp.
Hope this is of some help and I'm not just stating the obvious.