Generally a desktop, especially with a larger screen and speakers.
Laptops will generally vary between the low 20Ws up to around 50W, though some beefy systems like the Dell 17" XPS range (high end gaming laptops) can consume up to 150W. These high end machines only run at full speed when plugged in however and scale back dramatically on the battery.
On the desktop side, a standard machine will generally consume around 100-150W. However, with the ability to customise the power usage can jump dramatically. If you have a graphic card like mine, which consumes 190W by itself when under load, your overall power usage is going to be much higher. Add in multiple hard discs, dual graphics cards and all the accessories, and you can see why they make 1000W power supplies for them.
To make matters worse for myself, I also use my desktop on my plasma tv, which draws 565W...







