From professor Bart Ehrman's book, Did Jesus Exist?, page 42:
In short, if a historian were drawing up a wish list of sources for an ancient person, she would want a large number of sources that derive from near the time of the person they discuss: that are extensive in what they have to say about the person; that are disinterested*, to some extent, in what they say; and that corroborate one another's accounts without having collaborated.
*Earlier he had written:
The problem, of course, is that most sources are biased; if they didn't have any feelings about the subject matter, they wouldn't be talking about it. But if we find stories that clearly do not serve the purposes of the persons telling the story, we have a good indicator that the stories are (reasonably) disinterested.
Ehrman will proceed to show that there are numerous sources (at least 7) from near the time of Jesus (some within a decade); that they are extensive; and that they corroborate one another's accounts without having collaborated. But I don't remember his discussing their disinterestedness. I guess if I were going to take the mythicist position, this would probably be the weak link in the chain that I would try attacking.
And given that Ehrman himself rejects the resurrection story, and I think he rejects the miracle stories as well, one would want to know on what basis he rejects them, other than philosophical prejudice. I suspect he would point to their lack of "disinterestedness."
Update Two points: First, I remembered wrong on what exactly Ehrman claims about the historical sources. I better just quote him at length in a new post. Second, I'm not finished with the book, yet, and he's beginning to talk about he would call "disinteredness."