Two, I think. I think most participants will probably agree that there are two bland stouts (Beamish and Guinness) and two flavoursome stouts (Murphy's and O'Hara's), and that picking between them is the hard bit.
As someone who hates Beamish, I was quite gratified that so many of the Beamish-lovers couldn't pick out that alleged distinctive bitterness.
I'm also gratified to finally learn, for sure, that draught Murphy's tastes better than draught O'Hara's. We should write to Carlow and tell them to stop damaging their excellect stout. (Or put more chocolate malt in it. It's all good.)