I used to ride a lot of steep hills. On the steepest sections I would stand up to avoid loosing cadence in my lowest gear.
On big mountains with a loaded tourer I use MTB gears and spin. Often I sit back and use the muscles behind my knees more than usual.
Since I changed my commuter bike from a road style bike to a more MTB style I find it really tricky to stand and attack a hill. Im not sure why.