Can't top the speech from The Zygon Inversion. I normally don't take to Moffat's long speeches, but this was exceptional. Even Murray Gold knew to shut up and listen.
One of my favourite episodes, The Pilot, has a few of my favourite lines in it. His lecture at the beginning about the Tardis is delightful, befitting of a writer and actor who know the show inside-out; and when he tells Bill "You're safe in here, and you always will be". That's what I want from the Doctor.