I used to believe that Colin was miscast. I spent years hating his portrayal.
Funnily, I have actually had the reverse experience, CSM. I spent years absolutely accepting Colin as the Doctor (even loving the coat) and thinking that his woes in the role were completely the fault of others. But quite recently I have started to be less forgiving of his telegraphed acting; pulling faces and mugging responses to everything around him and the silly shouting. (Unstable?!? Unstable!!!?!?I am also profoundly unconvinced by Colin's retroactive claim that there was any kind of plan to "peel the banana" and show the Sidney Carton hero under this unpleasant exterior.
I think the mistake was in giving the role to an actor best suited to the theatre. Colin also tended to accept and happily go along with - and indeed relish - moments that pulled into question the morality of his Doctor. The acid bath quip for instance, which I think all the other actors in the Classic run would have refused to say - and Colin has said he wished he could have pumped more bullets into the Cybercontroller etc.
As a man he is witty, charming and a great ambassador for the show - albeit seeming to have a Tom Baker grudge. But as a Doctor, I feel he was as much the architect of his downfall as the forces around him.
I am also, lately, wondering more and more who could have been handed the assignment in his stead? It seems that JNT gave the role out on this occasion to the first person he found amusing in his orbit, when really he should - as a professional - have cast his net wider as a matter of form.
So, though it nostalgically pains me to do so, I now have to vote miscast for old Sixie.
But I have absolutely no quibbles with any of the other Doctors.*
*And, even though I feel that JNT cast Davison simply because he was flavour of the month and popular at the time, the fact is that Davison also happens to be a remarkable actor and was able to bring qualities to his Doctor that a lesser actor would not have.
(There remains to me the lingering possibility that, had Tom quit a year later, JNT might have cast a different flavour of the month actor who did not have Davison's talent.
So either JNT was astute or lucky in this regard. I am not so sure of his astuteness and am leaning more towards lucky.)