In college, I listened to some advice about choosing less experienced instructors because they have more recently been through the same material that they are teaching. Plus, they'd be more motivated and less jaded. Turns out that the experience factor is not that important.
At this point, after having many mediocre teachers and very few good ones, I've come to the conclusion that only a small percentage of "teachers" are actually worth learning from.
The only good teachers I've had were meticulous about their knowledge AND really loved teaching. Not one or the other.
It basically requires a full-time teacher. Anyone besides that is actually worse for me than no teacher because they are apt to ruin my interest in the subject. Maybe I'm spoiled, but most classes aren't much better than a textbook and a chat with a good friend.
Who does that leave as worthwhile teachers? Rare people like Feynman, a couple of instructors on Lynda.com, one or two from my undergraduate classes, and a couple from the new array of online classes. Again, you can be a grad student and be a great teacher, but you have to know your domain inside and out, and love teaching it. That means fielding questions with ease and, probably, being able to teach without notes if needed.
One of the reasons I like open online courses is that you get to experiment until you find an experienced professor who had enough initiative to start an online course in the first place. I really do mourn the downfall of the in-person class setting, but at least in my experience, a vast majority of them aren't what they're cracked up to be. Maybe at top 10 schools the situation changes?