Well I happen to agree with him on that one. You may not like Nesbitt (and I think he can be a bit smug sometimes) but the guy clearly has talent. If you didn't like him in Jekyll then check out his portrayal of grief in the final episode of Cold Feet, for example.
Starkers, do we know for certain that PD is his favourite Doctor? He's certainly very fond of him but Davison was arguably the last iconic Doctor of the old series before its popularity started to decline, as far as the mainstream audience was concerned, and is the only one of the surviving past Doctors (bar McGann, whose return wouldn't have carried the same weight) who still looks more-or-less like his Doctor. C Baker and Sly McCoy wouldn't have had the same impact, and Tom doesn't look recognisable as the fourth Doctor anymore. Although they explained Davison's ageing, he still looks very much like the same man he was 25 years ago, ie still slim and still very youthful-looking for his age, so that all you really needed was a throwaway line referencing his appearance. They could have approached Tom Baker and still given the same "time differential" explanation for his aged appearance, but while that would've been satisfactory enough in story terms it arguably wouldn't have had the same impact on the viewers.
Also, if PD is his favourite Doctor, that certainly gives me hope that he's not likely to cast a Tennant-alike next time. StCoop, I believe James Nesbitt has already dismissed claims that he's taking over the role, so you've got nothing to worry about there.
I read an interview with SM where he basically said Davison was the best actor to play the Doctor,you can also tell how from the heart various bits of Time Crash are, he seems to prefer an all action youngish Doctor. Happy for someone to offer contrary evidence but that's been my interpretation of various things he's said.
Now that you mention it, I think I actually read that one too, where he said Davison was "the first of the modern Doctors". Personally, my favourite of the old series Doctors is Tom Baker, but I can see Moffat's point that Davison was the best actor to play the role. I happen to think Troughton and Pertwee were on a par, mind you, but I see where he's coming from. I wouldn't say a younger Doctor constitutes all-action though. I like how PD played the role as a young man trapped in an old man's body, frustrated that no one took him seriously. 
