What do we mean by the word 'should'? To whose benefit are we speaking? The fans? The actors? The show itself (ie. its legacy)?

I think in general, whichever of the above we are talking about we can say that anyone who wanted to leave should have left. There's no value in having someone who is not committed.

That leaves us the Doctors who were 'pushed'. The problem here is we don't really know who these were. Hartnell is likely to have been one, Pertwee possibly, although there is no direct admission of it by anyone on the production team. Colin Baker is a grey area: technically speaking he was given the option of continuing into another season but under circumstances he didn't like and so he rejected the offer. McCoy was clearly not given the option to continue and circumstances dictated that McGann's Doctor was discontinued.

It's so speculative to wonder what would have happened had any of these stayed that it seems like a futile consideration.

I think the show's continued existence and continued success speaks for itself ultimately. Maybe in an alternative universe some things were different and the show is even stronger. But it's done pretty amazingly in this one and I think I will happily take what we got. Things have worked out great. Maybe not perfect, but if we consider all of those alternative universes... this one has to be up there amongst the best.

Pre Davison - Happy enough there were a lot of episodes.
Davison - at least one more year.
Baker - Hard one; the show really needed the change to McCoy but it wasn't Baker's fault. If he had been given decent scripts and direction of image (change of clothes, less bickering with companion etc) I would have loved him to stay for years (so another yay to Big Finish). If they had done what Big Finish had done basically... yep years of Baker. But it couldn't have gone on the way it did.
McCoy - Again lots more.
McGann - I would have loved a lot of years but not the ones the American company had in mind.
Eccleston - At least one more, but why not more?
Tennant - Again one more, I think it would have been ready for a change after that
Smith - Many more
I hope Capaldi stays for a few more as well.

McCoy should have lasted a bit longer, however what annoys me is that he never got two extra stories for each of his seasons. There's like six stories from his era that should have been made but BBC only wanted 14 episodes.

Give us some John Hurt. A separate animates War Doctor series.

As much as I love the conclusion to Peter Davison's time as Doctor, Androzani definitely leaves you with a feeling of "what could've been." Perhaps if he'd taken on the darker role intended for Colin in the succeeding season, rather than leaving, the original series may have had a significantly longer shelf life.

Ignoring the fact that I am ever so slightly biased as he is my favourite Doctor... I really do feel that Matt should have been given one more series. The way his departure was announced between the end of series seven and the 50th special meant we didn't even get a real penultimate episode to mark his era. Tennant had two years worth of fanfare and bells chiming to signal his leaving; Matt got nothing until Christmas Day. If he'd have done series eight it would have been bittersweet; knowing that he was going and that those were his final episodes. As it stands I felt that I never really got the chance to come to terms with his passing before it actually happened and I feel that I'm still trying to get my head around it now. I think this is probably why I've found it so hard to adjust to and accept Capaldi in the role.

Much as I would have loved Davison to stay another year, I like the way he left.

It left you wanting more and that's the best way to go, rather than hanging on long after you should have left.

[quote=Piipp;84168898]Ignoring the fact that I am ever so slightly biased as he is my favourite Doctor... I really do feel that Matt should have been given one more series.[quote]

? Smith was offered a season 4, he declined, As did Tennant.

Smith says he now regrets it,

Now it looks like they offered PC a 4th season

I think every Doctor bar one had just about the right amount of time.

The exception being the Eighth Doctor who should have had at least one full TV series to himself. It will always niggle me that he didn't get it. Failing that, he should have been The War Doctor. Brilliant as Hurt was, there was no need for another Doctor shoehorned in.

Of course, personally, I wish the Tenth Doctor had carried on until...well... forever, but honesty forces me to admit I think he was running out of steam by the Specials.

I'd like Capaldi to carry on with Chibnall, because hopefully he will get some decent stories.....

IMO, Hes got plenty of great stories, (Heaven sent, Listen, Zygon Inversion etc) But Id like to see what CC could write for him.