I chose an Apple MacBook Pro for various reasons. They have an excellent battery life meaning that I can usually have my main six applications running at once and get 4-5 hours of battery life. This gives me the flexibility to work anywhere for half a day before needing to find a power socket.
When I'm at home, I have a Matrox DualHead2Go which allows me to plug the laptop in and split the screen to my dual monitors. Along with a bluetooth mouse and keyboard, this set up gives me the flexibility of having a proper desktop experience with the option to just grab the laptop at any point, head out the door and still have all of my files and software with me.
There are seemingly minor benefits as well such as the operating system layout remaning fairly consistent in the 10 years since I've been using Macs, unlike Windows where things are continually moved and changes to the GUI are made just for the sake of it.