Have never used disc brakes but I have those cantilever things on the mountainbike. Hub brakes are heaven compared to them, you just install them and they work without maintance mile after mile, no fiddling with them and no need to change pads. And when I grip both front hubs I can stop on a dime, what more do you need?
Don't think there are much difference in weight, the brakeshoe arrangement on a disc brake must be built to take the strain with the accompanying weight