I've got Tennant 3rd on my list because I'm not a big fan of Pertwee. Although I don't agree that Tennant is better, I think I understand part of why it's being said.
Tennant has shown a larger emotional range than TBaker, mostly because the story allowed him to do so. We've never seen the Doctor show the kind of emotion as he did in the last scene with Rose in "Doomsday". Not even when that sniveling little whiner Adric died. :smilewinkgrin:
When I decide where they land on my list of best Doctors, I have to consider the stories they had. Colin Baker proved that a bad script cannot consistently be overcome by a good actor. Peri was not a good companion, but she had that same bad script as well. This is also why Eccleston really gives T Baker a run for his money at the top of the list. Eccleston didn't have a single bad story, while both TBaker (Invasion of Time) and DTennant (Love&Monsters) did. (BTW that wretched Love&Monsters is up this Friday on SciFi.
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As far as companions, I think Rose does top Sarah Jane for me. She was awesome in The Satan Pit. BTW, who are your Top 5 companions? Mine are Rose, Sarah Jane, Romana #1, Ace, and Captain Jack.
Oh, and I was watching the last episode of "Enlightenment" the other day. I don't understand why somebody didn't hand Janet Fielding (she played Tegan Jovanka) some onions and have her work up some tears when she thought that the Doctor and Turlough had been killed. I don't think she shed any tears when Adric died either. You can't tell me that somebody as fiery as she was wouldn't have bawled her eyes out when she thought, or knew, that her friends were dead.
I haven't seen enough of Hartnell or Troughton's work to make any kind of judgment about those guys either. I think it's worthwhile to note that they were strong enough to carry the show during the early years. Troughton, in particular, had a tough job to be the Doctor after Hartnell defined the role as the first one.