So, whats the best Doctor Who episode, and why is it Turn Left?

So, whats the best Doctor Who episode, and why is it Turn Left?
That's not how you spell 'City of Death.'
Which is technically four episodes, but one short, snappy, self-contained story.
I'm terribly sorry, Mack, but am babby little idiot, and have only properly watched Nu Who.
Tell me your Nu Who favorite, cause my old Who favorite is Genesis of the Daleks, obvs.
I shouldn't be such a prat about it, to be fair!
My favourite Nu Who is probably End of Time. It's a finale but it does a fun job of tying together a lot of really cool bits from across the series. Also, the bad guy reveal is really well done in context.