The question here is a unclear. Does the OP mean which college/university orchestra is the best (or which ones are good) or which conservatory has the best orchestra (and that question could be further refined to “which conservatory has the best orchestra for the purposes of students who wish to go onto to orchestral careers?”) These are very different questions. Folks on the Music Majors forum are more inclined to be able to answer the second two questions.
Also, for the first question, “best” is a problematic term, as it could mean many things. ClarinetDad, the OP, has posted a bunch of reviews of conservatory orchestras. This suggests he is trying to get us to compare conservatory orchestras. He might not realize, for example, that the Curtis Orch is a static ensemble (consistently the same players, more or less, because the school is so small.) But the Juilliard Orchestra is not a static configuration-- students are assigned to orchestra cycles and the composition of the orchestra is never the same from one cycle to the next. There really is no “Juilliard Orchestra”–it is a constantly changing ensemble. So it’s really apples-to-oranges. Of course an orch like Curtis’ will result in a tighter ensemble because they play together more. But Juilliard’s system offers a different kind of advantage: students get a wider range of experience.
As for orchestras in regular colleges, even if you could settle on what is meant by “best”, it would be hard to do a comparison with any kind of credibility or objectivity. A better question might be, what non-conservatory colleges/universities have good extracurricular orchestra programs.
As for conservatory orchestras, my understanding is that Rice and CIM are among the top programs for students who want orchestral jobs. And even so, my daughter’s friends, at other conservatories, are winning orchestra jobs right and left.