It's not going to be Cumberbatch or Freeman. To even suggest that is moronic. After the Hobbit and Star Trek, these two are going to be in high demand in Hollywood.
And it's not going to be Damian Lewis... why would he take a step backwards? He's coming off a pretty huge "serious" show in Homeland, and his role might not be done on it for all we know. It'd be kind of limiting for him to go do Doctor Who now. Popular as it may be, it's still a niche show.
And I don't think it'll be Hurt, although I can see him being the new River Song-ish mystery character for Moffat to work with here and there.
I see no reason to assume it wouldn't be a fresh face, given the direction Moffat went in with Smith.
Just for shits and giggles, though, I'm still hanging my hat on Paterson Joseph.