Harlequin v Cardiff was second only to the Harlequin Llanelli fixture when I was young.
My father took me to see the Scarlets play at the Cabbage patch several times as a youngster and I got to see some of my heroes play especially Derek Quinnell. Going to see Cardiff beat Harlequins was just as exciting, and it is there for the single time I saw him play live, that I saw Barry-John the great Welsh fly half play.