Question: why slytherin is the best house?
Answer: Slytherin is also the best house due to their house quality: ambition. With this trait, Slytherin people make sure that they stay alive unlike their counterparts in Gryffindor. Gryffindor's characteristic is bravery. Bravery might not seem terrible, but it is possible to be too brave (which countless Gryffindors are).