I definitely agree that the question is very tough especially with how well they have all been written and portrayed, oh how I would absolutely love to have them all be No. 1 because they are all amazing in their own little ways.
But I would have to say that Suzu is my favourite ever since you first get to see her in the school, but every other girl also deserves No. 1 because of the previous point where they are all amazing in their own ways