J.K. Rowling stated that Harry Potter would have joined Gryffindor, the Hogwarts house associated with bravery, courage, and daring. In the novels, the Sorting Hat places Harry in Gryffindor during his first year.
Hogwarts has four houses: Gryffindor, Hufflepuff, Ravenclaw, and Slytherin. Each is named after one of the school’s founders and has distinct symbols, colors, and reputations. Harry’s closest friends, Ron Weasley and Hermione Granger, are also sorted into Gryffindor.
Harry briefly considers Slytherin because the Sorting Hat detects qualities that could fit that house. His choice and character development are important to the series’ themes, but the canonical house assignment is Gryffindor. The question concerns Rowling’s stated view of Harry, not the house in which Rowling herself would have been sorted.