The other day I was browsing in a local record store and I found two Callas's recordings of Bellini's Norma: the first one is in mono sound, recorded in 1954 (Mario Filippeschi/Ebe Stignanini/Nicola Rossi Lemeni/Tulio Serafin/EMI Callas Edition), and the other one is in stereo, recorded in 1960 (Franco Corelli/Christa Ludwig/Nicola Zaccaria/Tulio Serafin/EMI Callas Edition). Price of the first set: about US$ 26.55. Price of the second set: about US$ 38.15. Which is the best one? Opinions, please. Wilson Pereira