Out of the 5 major parts of an application, what do top colleges consider to be the most important?

I think most of the top colleges will give the greatest weight to school record, both in terms of grades and rigor of courses since that represents 3+ years of work. From Yale’s website,

"Academic Ability

Yale is above all an academic institution. This means academic strength is our first consideration in evaluating any candidate. The single most important document in your application is your high school transcript, which tells us a great deal about your academic drive and performance over time…"

I also suspect with the huge number of app’s that many of these colleges have to sort through, there is some threshold, whether test score, gpa or a combination of both, something like the AI, that lands candidates quickly in the reject pile absent some significant hook.