Prefer Chiang on a purely personal basis (I really don't like Newsom, despite him ticking most boxes)
Newsom seems to be very unpopular at this forum.
Newsom is unpopular in a lot of places; he's regarded as untrustworthy and in the pocket of corporations. He's seen as too "slick", and some people think its inappropriate that he had an affair with the wife of a staffer. He's rightly praised for his marriage equality stance, but a lot of people feel he's too much to the right economically. Or at least that's the impression I've heard from Californians I've talked to on a few forums.
A few Californians I talked to said that they like Chiang because they don't see him as slimy like Newsom or Villaraigosa. They feel he's a lot like Jerry Brown; low-drama, good for California's economy, and not transparently ambitious. Plus they think it'd be nice for California to have an Asian-American governor.