Such a tough call to make as each brought their own magic to the role. However I lean more towards Capaldi. His journey echoed 1 and 6 starting as a harsh alien, turning towards a warm character at the end of the run.
Plus Capaldi had the banger of the episode Heaven Sent, which is such a masterpiece puzzle box.
Ahh the genius that is Elon Musk, I'm sure we're all cowering at his superior intellect.