The nicest is obviously the Retina MacBook Pro, but if you need lots of built in storage for cheap the classic MacBook Pro is best.
The Air is the lightest and so the obvious choice if you'll be carrying around with you all the time.
Thanks for all your replies!
Yep, that is exactly the reason I am tempted by MacBook Air, I'll be taking it everywhere so it does need to be light. However, I am not that sure there will be enough storage for all of my files.
Also, how easy is it to install Windows on a MacBook? Is it worth doing it or is it best to keep OS X?
If you're going to get the Retina MacBook Pro, wait a few weeks until the Haswell models come out. They'll cost the same and should have 50% (or better) battery life. If you're not, the Air is a great choice now since it already ships with Haswell CPUs.
If you're not going to use OS X as your primary OS, there might be better options for you. That said, installing and running Windows - either with Bootcamp or in a VM - is very easy and reliable. The only reason in my opinion to run Windows in Bootcamp is if you want to play games on your Mac, but if that's your primary use for the machine, you'd be better served by another laptop entirely.
FWIW I'm an Infrastructure Engineer at a mostly-Windows shop and I perform my entire job off of a 13" rMBP and a Windows VM.