Literally the whole soundtrack of Heaven Sent is just a work of art. Listen to the Series 9 album, disc 3 - it's actually amazing.

I Am The Doctor is my favourite

"Infinite Potential" is one of my favorites.

The Doctor's Theme from series one is my favourite Murray Gold piece of all time. I get chills every time. The Doctor's Theme Series 4 was still good, but it didn't quite have the same feel as the original. So I chose Doomsday, which is my second favourite Murray Gold piece of all time. The Shepard's Boy is probably one of my favourite post-Series 4 pieces though.

Other greats include: Father's Day, Madame de Pompadour, The Daleks, Martha's Theme, The Rueful Fate of Donna Noble, and Together or Not at All.

I like Clara’s theme.

I love the shepherds boy I actually learned it on the piano recently

@Talon1105 That's awesome! I've tried to learn at least the main parts of a few of the songs. So far I've got The Shepherd's Boy, Sad Man With A Box, The Doctor's Theme (RTD era), Clara's theme and Doomsday.

From the selection above, definitely The Doctor's theme. I really like that, while each New Who Doctor has their own individual leitmotifs, this piece of music represents the character of the Doctor as a whole as it is used for every New Who Doctor at some point.

My own personal favourite though is probably This Is Gallifrey just because of how familiar yet mysterious the piece sounds

Dark and endless dalek night

Obv its I am the Doctor