what are the factors that made Harry to choose Gryffindor instead of Slytherin?

Harry chooses Gryffindor because it is closer to his values and personality. A Slytherin is cunning and deceptive. They are ambitious and will take advantage of others for their own benefit. Harry does not like these values.

He might not have known fully what each house meant but he knew that Slytherin wasn't the house for him. Draco Malfoy also helped his opinion by being rude to Harry's newfound friends. Harry grew up not having much and being hated by those he lived with. Ron and Hermione were the first real people to reach out to him and want to be friends when Draco bullied them Harry's protectiveness showed. He wasn't afraid to protect those he cared about.