It's going to be Peter Capaldi. He's been in Doctor Who before playing the father in Fires of Pompeii and in Torchwood Children of Earth as Frobisher.
Honestly despite him being the bookies favourite I'd thought they were wrong, I wouldn't have thought that somebody who had such as major role in a Torchwood series who end up playing the Doctor and he is also signed up to play Cardinal Richlieu in the BBC adaptation of the Three Musketeers which airs next years.
Hopefully he'll look different enough from how he was as Frobisher when he takes on the role of the Doctor. That said I fully expect that fic will appear with Jack being rather disturbed by the fact that the Doctor's new face is that of the PM who tried to turn the UK's children over to the aliens. It's not something that I'm likely to write myself though.
All that said it will be interesting to see how they go with a much older (in appearances) Doctor, as Peter Capaldi is 55. I can't see them playing the romantic angle with early twenty-something companions with a Doctor who looks like they are old enough to be their father.