I can't think of many right now, but I'll try my best
Most Sympathetic
1. Dr Robotnik (Sonic X)- Sure he was sort of evil, but he did have his moments and sometimes could be very comical. He even helped out Sonic and even teamed up with him sometimes. In fact, in one episode, Chris and Cosmo were attacked and injured by a new villain. Dr Robotnik showed up and basically said "I don't like the way you attacked Chris and Cosmo! It's one thing to take them prisoner and threaten them, but when you actually hurt somebody, that's going too far!" Even when Sonic and Robotnik fought, Robotnik never fought to kill him.
2. The Toilenator (Kids Next Door) - Even though he wants to be a villain, he's not evil. He's actually kind of nice. Even if he is extremely incompetent.
Least Sympathetic
Frieza (Dragonball Z) - He's a heartless and sadistic monster who blew up 2 planets (almost eliminated an entire race because of it), enjoys brutally torturing his enemies before killing them, killed almost all of the nameks, and made Krillin explode. He also took Vegeta from his father when he was a little boy and said that if he didn't do whatever he wanted, he would kill his father. Even after Vegeta did everything that he asked, Frieza still killed his father. There's nothing sympathetic about that!