The best school for financial aid is the school that offers you the most financial aid or requires you to pay the least out of pocket. Among the 300+ boarding schools in the U.S., there are only a few that are notably generous in FA but most of them are very selective with thousands of applications each year or less selective but small with very few open spots when it comes down to your grade, your gender and the “silo” you fall into. That said, almost every school has a financial aid budget, so it’s possible to receive funding from almost any school you apply.
Of course, you can only apply to so many schools. So what should be the strategy? IMO - First, never mind about the school’s FA program and your qualifications. Filter out those you definitely don’t want to attend for whatever reason. Second, “cover the base”. Apply to those few that are on your wish-to-attend list and notably more generous in FA even though some of those schools may feel like reaches or high reaches. Remember some schools are reaches to almost anyone. But if you are in, the chances of your getting fully funded are very high. Third, do your own home work and apply to a sufficient number of “hit-or-miss” schools where you think you will be among the strongest applicants, which will improve your chance of being funded and/or receiving a merit-based scholarship.