As a person that lives in the town next to Stony Brook, and knows about the SUNYs I can tell you I had no clue that UMass Amherst was ranked about SBU at all. SBU has a great reputation and is highly regarded in many fields, especially the sciences. They have an incredible teaching hospital on campus that many of us in the county utilize. There are very, very bright students there (and I’m sure some less so).
Due to the hospital and staff at the univ, there are many people of different ethnic backgrounds there. Diverse student population as well. Not sure if you care, but there are 2 Indian restaurants not far from campus. One is fantastic!!
Good luck to you at either UMass or SBU.