Putting academic considerations aside, which school alumni network do you consider more important - one of GLADCHEMMS, or one of HYPSM (or other famous university)?
When I lived in NYC and worked on Wall Street I was always amazed to observe how many alums of elite Prep Schools would don their school sweatshirts, play Football or Ultimate or Lacrosse on weekends or evenings in Central Park, and then grab a bite afterward. Or go out for drinks. Or tailgate. Or just hang out. Their social interactions seemed far more prevalent than those of undergrads from HYPSM (although in truth, the Princeton alums did seem to hang out together as well). One of my roommates was a HADES grad and he and his classmates were extremely tight.
I am a grad of a non-famous college who subsequently went on to HYP and Northwestern/UofC (cloaking my identity) for grad school degrees, and it has always struck me how incredibly close Prep School classmates and alums are. The products of Hotchkiss, Deerfield and PA I hung out with made me a little envious how they seemed to try and help and pull for one another, whereas my grad school peers always seemed to be a little competitive, often comparing their trajectories. My grad school alums sure weren't eagerly feeding us any info that would help us get ahead.
One of the biggest reasons I want my kids to go to a top Prep School: for the future ties that bind.
Plus, as @ChoatieMom
correctly points out, "BOARDING SCHOOLS PROVIDE AN OUTSTANDING HIGH SCHOOL EDUCATION. THEY ARE NOT SELLING ADMISSION TO ANY PARTICULAR COLLEGES. THEY PREPARE STUDENTS TO HIT THE GROUND RUNNING AT WHICHEVER COLLEGES THEY ATTEND."