As much as I agree that a live class with real people has distinct advantages, your chances of finding a teacher on the level of Robert Greenberg is about one in a million. I think he's the most entertaining, animated, informed and overall superb teacher alive, and I say that as a fellow college instructor with a critical attitude toward most of my peers.
I just finished his Life of Beethoven series, and am now beginning the lectures on the sonatas.
But whether you purchase Greenberg on Beethoven or any other subject, you'll be glad you spent the money. He never stops giving interesting insight, and he can make you laugh out loud while you're learning.