Definitely the Shelbourne.
Great hotel and handily placed for one of the finest pubs in Ireland, Doheny and Nesbitt's in nearby Baggot St.
It's influence in recent Irish history is captured in this NYTimes article and the Guinness is excellent too.

http://www.nytimes.com/2009/01/04/bu...iger%20&st=cse

Toner's just down the road is great too as is McDaids which is a short walk away.
I really must get to see more of Dublin that just pubs !
Actually, while I'm at it this is my favourite pub in Dublin.

The Bull and Castle Gastropub and Beerhall, Christchurch Place, Dublin 2

The Bull and Castle is at the epicentre of Ireland’s growing craft beer trade is also a superb steak restaurant, owned by the FXB chain. There’s something for every occasion — from tasty beer snacks of cocktail sausages or chicken wings, through to pub grub classics like pies, steak sandwiches and bangers and mash, right up to the full T-bone or fillet steak. The meat from FXB’s own farms is as delicious as might be expected. The back of the menu recommends beers that can be paired with the different types of food, and the vast selection of top-notch Irish brews and quality imports mean there’s a beer here for everyone.