A great resource for almost everything you’d want to know can be found here: The Guinness Beer FAQt and Folklore page. For instance, many people likely don’t know that there are at least ten different types of Guinness (Stout) actually available around the world.
(Most—if not all—beer geeks are aware of this fact, though I must say I was interested and surprised to find out, for instance, that in Nigeria Guinness is made with sorghum rather than barley.)
The Extra Stout doesn’t suffer from these drawbacks; instead you’ll get a richer, maltier ale with discernible roasted malt notes, maybe some coffee, and a nice benchmark for what a Dry Stout should be. Also more of a kick: 6% alcohol by volume compared to Draught Guinness’ 4.2%.
Of course, part of the fun of the Draught Guinness is the novelty of the nitro widget, and everyone should try one at least once just for the fun of it. But if you’re looking to try the world-class representative of their beer, then seek out the Extra Stout. You won’t be sorry.