Portable Gaming: LAN case or Laptop?

I have AU$3000-3500 (that's US$2400-2700 at time of writing) for a new gaming system. Considering that I spend every other week at a friend's house, I would greatly prefer a portable system.
However, whenever I ask for the opinions of my friends, their responses tend to fall into two groups:

1) OMG LAPTOP = WIN CUZ IS SO PORTABLE

A) OMG DESKTOP = WIN CUZ IS SO POWERFUL*

*Note that if I were to get a desktop/LANing PC, I would have to spend like AU$500/US$400 (from the starting AU$3000) on a small and cheap laptop for school - suggestions would be appreciated.

So, my question to the community is twofold: which is better, laptop or LAN case? And, given one or the other, which model or setup would be the best value for my budget?