the guinness draught has the nitro widget in the bottle or can and that simulates the effect of getting the guinness out of the tap at the local pub. it's a much smoother, lighter pour.
the extra stout is thicker and heavier, with a lot less carbonation.
I have been drinking the Draught for awhile, but I had a Stout the other night and really liked it. It tastes more like Guiness to me than does the Draught bottle which has a funny taste, IMO.