Define "The Best". Is it the team that wins the most games? The team that does the best job of developing the kids to play "at the next level". The team that does the best job getting the kids in the right places to be seen?
IMO there is no reason for a 9YO to be too concerned about being on the best team. They should be playing on the team that gets them the most on field time and provides good development through coaching. Now if the goal is to play in college (which it should not be at that age) and your path to college runs through a program which is difficult to make at the older level as spaces are locked up at a younger age then you may want to consider getting involved in that program at a younger age.