Three Seasons is not enough.

I don't think Tom's record will ever be broken, just because of how gruelling the filming schedule is reported to be and the fact it's such a big role nowadays the lead will get a load of offers of other stuff they might want to do but can't due to the schedule. 

Personally I think both Smith and Capaldi could have done one more each, but 3 is decent enough. It gives a nice three act character development, and I suppose the old adage is to leave your audience wanting more... 

I'm of the opinion that each actor has had the part nailed by the end of their first season. The trouble with that is that playing a part like the Doctor - a 2000+ year-old adventurer in time and space - is that it's really hard to essay anything new with the character. Each incarnation has its own personality quirks - jellybabies, celery, recorders, velvet, strangling companions, etc - but the problem with playing anyone for a long time is that the challenge wears off and you start to repeat things. Nearly every actor playing the Doctor has left when they think they've had enough or before they think the audience is tired of them (and remember I said "nearly"). It's a tribute to the quality of the actors and the part that they can recognise that they don't want to become stale or boring. And, as others have said, I'd rather be left wishing they'd done more rather than thinking they'd held on for too long.

That's certainly one of the reasons why Patrick wanted to leave - and why Pertwee walked into a better schedule - but Troughton was gone anyway. Derrick Sherwin's on more than a few of the DVDs saying that the Beeb weren't too fussed about bringing Who back in 1970 but when they decided to, they wanted a new man for the colour relaunch and wouldn't have let Pat stay if he wanted - he'd be Hartnelled essentially.  

Given some of the latter-Troughton ratings, being objective because the man is a God to me, you can see why. Untill the Trial season and McCoy era, Pat had the worst ratings the show would have. Again, the new broom was needed to clear the decks. I'd rather watch Troughton than Pertwee anyday but hard to argue with the increase in viewers.

Just by-the-by...ratings fascinate me...the next time someone says how much of a joke Colin's Doctor was, remind them Colin in his first year managed significantly better ratings than Tom Baker did in his last and was pretty much exactly the same ratings draw Jon Pertwee was in his first year - and Colin was up against 3 channels, Tom and Jon only against 2. Colin also got better ratings in his first year than Peter Davison did in 1983 for Series 20. To use the famous JNT-ism,the memory cheats. People often talk about Colin's era as a disaster but it started out as something of a hit  -which is what makes the attempted cancellation even more bizarre and quite baffling.  

I'm not sure that's the case now though, 30 years on. I think its just that there's a narrative about Colin "failing" which looks correct retrospectively - the show was essentially cancelled while he was the Doctor and on it's reprieve, the Trial season, it did worse than ever ratings wise. But somehow that's just the story that people now believe to be the case and ignore that successful first year ratings wise. Essentially the second part of Colins' story has somehow become the whole story in pop culture - and even among fans.

I bet you there are loads of fans even on here who maybe aren't as schooled in the behind the scenes history that didn't know Colin got better ratings than chunks of Tom and Peter D's eras or did the same viewership as the glorious first Pertwee year.  I've rarely seen Colin's positive ratings mentioned even here where we're almost all big fans of Ol' Sixie but I'd not say it's people seeing what they want to see.....most just haven't heard the real story. We can but point out the truth in the hope that more people know it going forward.  

More ratings data:
Sixth Doctor
Top 10:
The Mysterious Planet: Part Four (3.7)
The Mysterious Planet: Part Three (3.9)
The Ultimate Foe: Part One (4.4)
Mindwarp: Part Two (4.6)
Terror of the Vervoids: Part Two (4.6)
Mindwarp: Part One (4.8)
The Mysterious Planet: Part One (4.9)
The Mysterious Planet: Part Two (4.9)
Mindwarp: Part Four (5.0)
Mindwarp: Part Three (5.1)

Bottom 10:
The Twin Dilemma: Part Three (7.0)
Vengeance on Varos: Part Two (7.0)
Attack of the Cybermen: Part Two (7.2)
Vengeance on Varos: Part One (7.2)
The Mark of the Rani: Part Two (7.3)
The Twin Dilemma: Part Two (7.4)
Timelash: Part Two (7.4)
Revelation of the Daleks: Part One (7.4)
The Twin Dilemma: Part One (7.6)
Revelation of the Daleks: Part Two (7.7)
Attack of the Cybermen: Part One (8.9)

Doctor Averages:
First Doctor: 8.5 million (134 episodes)
Second Doctor: 7.0 million (119 episodes)
Third Doctor: 8.2 million (128 episodes)
Fourth Doctor: 9.3 million (172 episodes)
Fifth Doctor: 7.9 million (69 episodes)
Sixth Doctor: 6.1 million (31 episodes)
Seventh Doctor: 4.8 million (42 episodes)

It really is context!  You have your Top Ten and everyone expects to see Tom in there, but standing shoulder to shoulder with him is Hartnell!  

And then - to add to the "context thing" - the 1979 stories aired when ITV was on shutdown due to strikes so essentially Who was unopposed in the timeslot meaning we can't really point to them and say it was that popular a year since the option was watch it or turn the telly off. There should be an asterisk next to them.

It's like I was saying, Colin's era is considered a failure because of what happened later but the truth? He started out strongly and kept solid ratings throughout his first year - and the worst ratings of his first year? One of the eps with Troughton which "only" got a 6.0.