For PC's....
Cheaper
More varied software available and usually free
More customisable
Easier and cheaper to rebuild and upgrade parts in
Against...
Painfully slow start up and shut down times
More prone to cyber attacks and anti virus software can make it run slower until fully scanned
Often less stable due to third party hardware
For Macs...
Super fast start up and shut down
Excellent design and build quality
Multi operating systems can be installed and run on the same machine - including Windows
iTunes works seemlessly on it and iphone integration is effortless
Swapping hard drive and Memory doesn't invalidate the warranty and instructions provided by Apple for doing so
Nice trackpad that uses gestures to speed things along (on macbooks)
Completely silent unless under a heavy load of processing (which kicks the fan into gear)
Against Macs...
Expensive
Although it can run Windows alongside OS X, it requires a 2 buttoned mouse to use it efficiently.
Limited software in many areas and often expensive options when available
Less customisable
The Mac route can be a time consuming and frustrating experience learning to use one as efficiently as a Windows machine, if you've never used one before (like it was for myself, until I bought one), but once you grasp it and get set up working as you want it, then Windows feels like an old modem taking forever to load when you fire up a Windows machine.
I think the bottom line is knowing what you want to do with it, then looking for the best machine that fits that criteria.
If you tell me what you're going to use it for then i'd try to advise you better mate, ie
For games - Windows
For music creation - either
For quickly checking your emails and web browsing - Mac
