The most beautiful version of Sammy's Bar I have heard live is from our own Mudcatters Linda Kelly & Pistachio (AKA Hissyfit).
I am not an a capella fan, but when I hear these 2 do it (well it just blows me away).
They did it live at my old club Market Rasen Folk Club on a charity evening "A tribute to Cyril Tawney" when he passed away.