have to be two of my favorite characters from the Harry Potter series. This topic has only come about because I have finally finished reading Chamber of Secrets and am now onto Prisoner of Azkaban (goodbye Lockheart until book five where he is funny beyond belief).
Prisoner of Azkaban has to be my second favorite Harry Potter book (the first is Sorcerer's Stone because without it, there would be no Harry Potter). In it you meet all of the exciting characters and begin to understand why exactly Snape hates Harry so much. Plus Ginny isn't so stalkerish and you find out that she actually has more to her character than just "OMG! HP is in the room! I don't know what to do!" Don't get me wrong, Ginny is one of my favorite characters as well. It's just that she wasn't very rounded in the beginning of the series (I like her best in book five).
Between blowing up his "aunt" and running from a "murderer," Harry learns so much more in book three than in the previous two books (but still not everything, oh no, not everything).
In a side note that is related, I'm a big Sirius/Remus shipper. Yes, I know Remus marries Tonks, but before that it was totally Sirius and Remus. Just read fanfiction, it will set you straight (I will go down with this ship).