Gee, it's hard to choose because I had so many wonderful professors my 8 years in the seminary, but I guess I'd pick Father Robert Mueller (which is pronounced "Miller" in Milwaukee). He taught me 2 years of German and music in high school and college. In the evening, he'd walk the halls and talk German with his students, and I still remember all the German drinking songs he taught us. It sure made things easy for me when I was trained as a German linguist for the U.S. Army (and kept me out of Vietnam).
I wasn't good enough to join the seminary choir, but he sure made them sound wonderful - and he led the choir with a gentle hand.
-Joe Offer-