A pole mount is the most efficient as the panels can be aimed a little easier. On the roof they are not taking up yard space which is sparse for some. I have mine mounted both ways as originally my thinking was they would be safer up there from someone looking for free ones. Larger panels aren't easy to walk away with once mounted and dismantling takes more time then most would be thieves are willing to spend. I've recently attached several to my deck as well hoping to move them latter to a pole. While in at my local solar supplier ( who does a lot of grid tie installs) we got talking about roof mounts verses pole mounts. Seems with Grid tie setups becoming so popular the fire departments have stopped attempting to put out houses fires with panels mounted to the roof. They just watch the place burn and make sure no other structures catch. Looks like all mine on the building will be moving shortly. If insurance companies get wind of this many with roof mounts could see their rates jump.