O'Hara's beceause a) it tastes of stout and b) because it's made by an Irish company. But mostly a).
Ken, you can get O'Hara's on draught in Ely CHQ. They don't do Guinness.
Dave, I think it's a brilliant plan. Especially given that Guinness is made by them Dublin ones and you wouldn't know what they'd be putting in it. You'll need big posters saying "No you can't have G*****ss: you're in Cork now, boy".