Jessica Hische gave an excellent talk at An Event Apart in San Diego:
I’ll answer the question that every person in the type world is asked—“What’s your favorite font?” If you are a designer of any sort, you’ve probably been asked this question more than once. I know there are plenty of people that can easily name their favorite typeface (usually Helvetica) but I’m not one of them. I’m a believer that if you have a favorite font, you’re probably using it inappropriately or way too often.
She has so kindly put an overview of the talk up on her website—If you are designer, it's definitely worth a read.
(illustration by Jessica Hische)