How can they ask you to only talk about one of your favorite shows? Doesn't everyone want to talk about more than one? But this is probably the only time when I would be able to tell what my very favorite of something is. When asked my favorite food or movie, there's no definitive answer, but favorite show ever? Arrested Development, hands down! I have watched all the episodes several times and don't ever tire of them and they make me laugh so much.
But a few other favorites:
Freaks & Geeks
What Not To Wear (I *love* makeovers!)
The Daily Show with Jon Stewart
Cougar Town (for reals, y'all, it got really good)