Well its a difficult decision. There are many Pro's and Cons of both. Let me run you through a few.
Mac:
Pros
1) There's no need to worry about all these viruses, adware etc!
2) It runs well and i've only ever frozen the computer ONCE!
3) The whole design looks very good. For example the dock is an awesome way to keep your frequently used applications.
4) Very simple to use
5) Lots of great built in programs such iMovie which is a good Windows Movie Maker and Garage Band which is very handy for me.
6) It's very fast and you can get some pretty decent specs.
7) A very stable OS and many cool features in each new one.
Cons: (bare in mind some of these can be conquered by running an emulator which can be very successful if you have an actual Windows CD lol)
1) Not many games are available for it.
2) If you're used to having a right click you may sometimes get confused when having to click and hold control to right click! Easy way round this just use a normal mouse!)
3) You won't be able to get some of your favourite programs on it.
4) Just generally the compatibility between windows and mac (without an emulator)
5) Most importantly they are expensive
Windows
Pros:
1) almost every game runs on it
2) almost all programs run on it too
3) More hardware customization available
Cons:
1) Viruses, worms, spyware, adware :O!
2) not as "sleek"
3) All those error messages!!!
4) OS not as stable. No cool features such as spaces!
Overall, I love macs but you could say they are a little over priced. You do get a solid OS and no worry of viruses. I have a windows computer as well and just get frustrated when using it! Macs can do some very professional stuff and always performs well.
As for model, it depends what you want laptop or desktop? The website as an easy custom build when ordering. Even if you're not getting it off the net you can still use it to see all the options you want with your computer and what it will cost. I'm not a whizz when it comes with all the techy stuff but if you've got the money i'm sure you could get an amazing computer!