I saw Draco as the most tragic character. He was being manipulated by his parents for their own social, power status, and egos. A child is always going to want to please their parents, even abused children often have a hard time letting go of that desire to please them.
Snape was an adult who made a bad decision out of jealousy, and hate. Old No nose, may have manipulated him some, but he was an adult fully responsible for his choices IMO.