Guinness is the stout of choice in Dublin, brewed as it is on the banks of the River Liffey which runs through the heart of the city. I first started drinking it around the age of 20, I think, having cut my teeth in beer drinking with dreadful Irish-brewed versions of American and Australian beers and lagers. For a long time Guinness had been perceived as an old man's drink, but through successful advertising campaigns in the 1980s it began to reach a younger audience. My dad was a Guinness drinker, draft pints, and I remember my grandfather - on my mother's side, a Dubliner - drinking Guinness which he poured from a bottle.
The thing about Guinness that surprises most people who've yet to try it is that is it light. The body is light compared to many beers, and it doesn't contain many calories. However, the taste is a little bitter, which led many novice drinkers to cut it with a little blackcurrent cordial, such as Ribena (a concentrate of blackcurrant juice and sugar). Living in the States now, I don't see this custom at all, as blackcurrent is not a flavour that is really in the mainstream, and I'm hoping the practice has died out back home!
I happily admit though that Guinness is not my favourite stout, even if I'm betraying my Dublin roots. I'll probably go with Murphy's, brewed in Cork, for that. You can get it quite readily in a few New York bars (Molly's Shebeen on 3rd Ave and 22nd St pours a nice pint). It is not as bitter as Guinness, so maybe a little more approachable as a first stout. Then there's Ireland's other brand of stout, Beamish, also from Cork, and in a distant third place after Guinness and Murphy's in terms of popularity and availability. I consider Beamish, which I really like, and I'll jump on it if I see it on tap, to be the RC Cola to Guinness's Coke, and Murphy's Pepsi.
Whichever stout you drink, always make sure that it is poured correctly, and that you drink it correctly. It is poured in a two-step process, the barman leaving it to rest after it is about 2/3 - 3/4 full, before topping it off. My advice is not to order it in a US bar where they're all about volume and filling glasses and pitchers with Budweiser as fast as they can. Once your cold pint is placed in front of you leave it to rest until it is completely settled. All motion should have stopped in the glass, and there will be a creamy white head on top of a deep black liquid - you'll see the colour go from a dark brown to black as the head settles. Now you're ready to drink. Don't sip. Take gulps. The head will leave rings down the glass as you drink, and when you're finished you should see about 8 to 10 rings. Enjoy!