Who do you believe? Saadia or Kematu? Personally, I believe Kematu. But that doesn't matter any more. Why? Becuase if you end the quest in Saadia's favor, the game is bugged to permenantly place two Alikr warriors at Whiterun's front gate, precisely where the vampires spawn! So by killing Kematu you in effect have hired a couple extra guards for Whiterun. Hopefully this will make Adrianne a little less likely to die. (That is, if the vampires don't spawn inside the gate where I can't get at them. )

Kematu. Saadia's story is full of holes, for example, she says she is being persecuted for speaking out against the THalmor in Hammerfell. That makes no sense since Hammerfell seceded from the Empire and is an independent nation now.

Solitude is the best city if you did the imperial quest line. Reason being is that they have Imperial soldiers, Solitude guard, and Pentalous Octulos all guarding the city. In the front have of the city when you enter the interior cell, there is also Jaree (if you didn't do his quest) and he can't be killed.