I hate coding on anything but a laptop. Having the keyboard + trackpad + monitor in such a tight space greatly decreases the time my hands and eyes spend moving. I've tried dual-monitor setups before, but they make me feel like my head is on a swivel.

Additionally, with a laptop, I can take my primary work environment with me everywhere I go. Coding at a coffeeshop or in the car is the same as at home at my desk; you can't do that with a desktop and multiple monitors and a mouse.