I’ll just echo some thoughts.
I agree if you are already above a really comfortable budget, the extra stretch for CU is probably not a good idea unless your kid really, really want to be in Colorado (and even then, at some point you have to draw a line on what is affordable, and it is not like Colorado is going away in four years).
Pitt and UMass Amhest are then both perfectly good choices, both for pre-med and also if your kid ends up deciding to do something different, perhaps very different.
So if it were me, I would suggest setting is really the key factor. Amherst is a classic college town with lots of other nearby college students. But it is otherwise fairly far from a really big metro (so I am not including Springfield or Hartford, say). However, it is like 2 hours or so from Boston, and that is potentially day trippable, certainly close enough for weekend trips.
Then one of the reasons some people like Pitt is the part of Pittsburgh it is in (known sometimes as the East End) can sort of feel like an overgrown college town itself, and there are lots of other colleges in that area (including CMU, and you can take some classes there incidentally, or in fact other area colleges). But the rest of Pittsburgh and its related amenities are all right there too.
I really don’t feel like there is a right or wrong answer here. In my experience, some kids struggle with the idea of being more than a couple hours away from a city like Boston, and that’s perfectly fine. Others love the idea of being right in a fun, historic city, and Pittsburgh is enough of a city for them.
For a little perspective, the Boston Metro is a little over twice the size of the Pittsburgh Metro. The Pittsburgh Metro is then a little over twice the size of the Hartford Metro.
Does that make Pittsburgh too small? Too big? In the sweet spot? Totally subjective, of course. But I would see that as the most obvious consideration.
Incidentally, that does spill over a bit into convenience of experience opportunities and such, but I would view that as more of a minor factor. Plenty of people at UMass, or indeed other Amherst area colleges, figure out how to get the experiences they need for med school. So being in the heart of a ton of walkable hospitals and such is nice for Pitt pre-meds, but not at all required for pre-med success.