I personally don’t find rankings and lists to be truthful about what schools are “the best”. You don’t know how these lists are being curated beyond who publishes them. Schools like Juilliard and Yale always top the list (rightfully so-- they have incredible programs but also huge endowments).
Both Emerson and Mason Gross are phenomenal programs with solid connections in the industry. Boston is not an “agent” town like New York and LA. It’s community is strong and supported by local actors where you don’t need an agent to get in the door like NY/LA. Where does your brother want to end up? LA, Boston, New York, London? While many programs push a showcase for agents for final-year actors, Boston schools don’t always do this (not sure if Mason Gross or Emerson do.)
Your brother should look at course sequences for training to see how he will progress through the program. Like others have said, some schools offer a wide range of techniques (a “toolbox” to pick from), while others focus solely on one methodology or pedagogy (Looking into the background and education of the faculty is also important for this reason. If all the teachers went to the same grad program… the teaching will not be very diverse, in my opinion). Some schools have long-standing tenured professors, while others rely on a massive pool of adjunct faculty that shifts constantly (NYU). Some schools may allow you to take a few electives outside your major, while others only allow you to take electives from a curated list within your school. Some schools solely focus training on acting, while others allow students to explore other avenues like directing, production, film, creative writing, etc. Many programs are shifting their focus to incorporate film, digital media, and production into their performing arts programs. Some are not. Mason Gross incorporates a semester in London into your program. Others do not. There’s a lot of digging your brother needs to do into what he wants to study and what schools will suit him.