Econ majors at Michigan often have the same opportunities as Ross graduates so don’t feel that if you end up at UM that you’re going to be limited in that regard. Note however that Ross classes are large classes, so they may very well be in Econ as well.
If you’re looking for small classes, you may want CMC.
You shouldn’t put the cart ahead of the horse for Penn at this point since RD isn’t out yet, but if that comes into the mix then that may change the ballgame for you. However, you’re looking at 3 completely types of schools, settings and sizes.
If you have AP credits that may also be a factor. Penn won’t take many and will just put you in higher courses. Are you ok with that?
Are you interested in a large rah rah campus, or much smaller? You should talk to students (not parents) at each school and see how they feel. What they like and dislike at each. How hard is it to get into classes. Can you graduate in 4 years? How easy it is to get to the school from where you live. Can you graduate early, or double major, minor, etc.