This is more of a request for advice, since I think there probably is no canon answer. If I was to watch a Doctor Who marathon, and include the animated episodes Dreamland and The Infinite Quest, what would be a good place to put them in the episode order?
As Martha is traveling freely with the Doctor, the story may be set somewhere between the series three episodes "42" (which follows directly on from Martha's invitation to long-term travel in "The Lazarus Experiment") and "Utopia" (which begins the series finale). However, the Character Bios on the DVD release state that Martha is traveling with the Doctor for one more trip, which seems to set it before "The Lazarus Experiment". Wikipedia
In an interview with DigitalSpy, Phil Ford (the show's writer) has categorically stated that Dreamland takes place immediately following the special episode "Water of Mars":
Where does it fit in the Doctor's timeline?
"It's set after 'Waters of Mars'. It's a much more light-hearted story than 'Waters of Mars' or the story that will follow it. As I think Russell said elsewhere, just because of the dark ending of 'Waters of Mars' it doesn't necessarily mean the rest of the journey is going to be doom-laden. The Doctor stops off for a bowl of chili - the kind of chili you could only get in an American diner before 1962, as he says!"