Windows:
Pros:
Cheap
Compatible with 90% of software and games
Very stable
Cons:
Looks like shit
Software, including OS, can be expensive
Malware if not careful
OS X:
Pros:
Beautiful UI and animations
Lots of great software for free and in general
Very stable
Very secure
Fast
Cons:
Expensive as balls
Good, but not great compatibility
VERY VERY EXPENSIVE!!
Linux:
Pros:
Geek status
Can look slick and beautiful
Extremely customizable
Fast
And the list goes on( see cons )
Cons:
Has the compatibility of a rock
Has many great features, but 90% of users can't / don't / has no reason to use
Over rated( because, as stated, most of which what makes Linux stand out, user don't ever use or simply can't use. )
Can be difficult to use if new
Can halt / freeze / crash / panic / die / BSOD-ish if not used correctly
Just my humble opinion