I would have to say Von Karajan. He has conducted some of my favorite opera recordings. The live Trovatore with Price and Corelli, a great cast giving incredible performances, the Callas Lucia live from Berlin in 1955, and the Bohème and Butterfly with Freni. There is the 1960 Salzburg Rosenkavalier and the 1957 Falstaff with Gobbi. He had so many accomplishments, a power-driven conducting technique, and he really connected with his musicians. His conducting produced a constant, natural pulse and he created sweeping crescendos.