Laptops are more environmental friendly than desktop. It consumes five times less electricity.
Desktop computer usually uses around 130 watts while a laptop only uses around 15 watts. If you buy a desktop, get an LCD screen. Enable the power management function on your computer.
So if you are planning on getting a new computer you should consider a laptop instead of a desktop computer.
Other good things are that laptops are smaller and use less packaging, meaning less transport and storage space needed.