On our works driving course we're taught to use both brakes when stationary.
Handbrake on to prevent/try to stop the vehicle shooting forward if hit from behind. In neutral to prevent the gears from being stripped if the same should happen and your foot comes off the clutch. The reasoning behind the footbrake too, is in case someone is driving in a daze behind you and fails to notice you stop (or just not realise it for some reason), then the big, red, glowing lights on the back serve as a further, positive reinforcement that the vehicle is, in fact, stationary.