I am hoping some voice/composition folks chime in, because my son is a classical instrumentalist so his experience at these three programs would be quite different.
Some general thoughts:
He attended Interlochen after sophomore year in HS. For my son it was transformative. Very high level private instruction on his instrument, excellent studio class and several master classes, heavy emphasis on reed making, high quality large ensemble and small ensembles. He also enjoyed being with students with other artistic specialties as they have dance, visual art etc. Beautiful but very remote area. He did not love the cabin lodging (without air conditioning). I do not know if this has been upgraded.
Mine only did the BUTI intensive. This was after junior year. Conservatory type schedule and dorm rooms. For some reason my son did not love BUTI, perhaps just not the right fit at the right time in his life.
He went to Brevard after his first year of conservatory. Only a small number of college age students were accepted as they limited the enrollment due to the pandemic. So his experience is likely not representative of a normal summer there. He felt the private lessons and studio classes were high level, really enjoyed his small ensemble and coaching. Orchestra was wonderful as well especially as he had been remote learning for the entire year prior. Really beautiful setting, rather rustic but fairly decent accommodations. Big bugs and snakes. 
I think when you look at summer programs, it is important to consider your kid’s age and how challenged they will be (and how comfortable they are with these challenges)
Feel free to message me if you have other questions.