I really like the one with Van Gough. (I don't remember what it's called.)
I adore Blink and 42. Those always scared me as a kid.
I can't pick just one!
Probably Silence in the Library. I thought that was a really good episode.
But I also really like Blink, The Empty Child, The Impossible Astronaut, any episode with The Master, The Stolen Planet, Planet of the Ood, and Day of the Doctor.
I have a lot of favorites.
Dr. Who, Supernatural, Sherlock, (yes, because i am that predictable), Drop Dead Diva, Modern Family.