Standardized test
Extracurricular activities
GPA
Hi! I'm also applying to MIT, and the answer is all of them! Each piece is a piece of data for your admissions officers, and since they have a holistic approach to evaluating your application it's hard to say what matters more to them. Overall none of these individual factors should make or break you, as letters of recommendation, essays, and coursework are also all important in their reviewing process.
To keep this community safe and supportive: