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.
I believe there was a report saying that they're changing policy to allow moderators to be voted out. If true, to me if they are announcing something so drastic, which can be manipulated by bots, then there is an impact of some kind.