1. Saucy Jack (the Ripper) from books 3, 4, & 5 of Alex Grecian's Scotland Yard Murder Squad series. He's written as a vile human, but I've got to admire his tenacity, snark, and creative butchering. Prof. Umbridge is just the literal worst so I get no joy in hating her. Lucius Malfoy might get second place.
2. Plot. I can overlook flat characters for good plot but I care less about super deep characters doing nothing but sharing feelings.