I'm only half serious in asking this, because many of the best comedies have been produced by a combination of actors and writers from different parts of the UK. For example, Alan Patridge is the product of two Englishmen (Steve Coogan, Patrick Marber), a Scvotsman (Armando Ianuci) and a Welshman (Peter Baynham). However, does anybody think one country is inherently funnier than another? If pushed, I would say England is head and shoulders above everybody else in the union. In fact, it's barely even a contest.
And as for Northern Ireland? I can't think of a single funny person from there other than the Reverand Ian Paisley and those guys that go marching in bowler hats every now and then.