My favorite prefect is Max MacTavish. He seems like he used to be a jock, and he's the only prefect who will apologize to Jimmy if he bumps into him. Plus, he's more of an authority figure than a blatant abuser (although I still like his insults).
I also like Edward Seymour, but for pretty much his dialogue. (Edward: "Yow, MY NARDS!")
My favorite officer is Officer Williams, because he seems like he genuinely cares for the kids. He'll even drive kids who break the law during school hours back to school. However, he can be seen making deals with Mihailovich...