If those were my choices, I'd pick Cambridge hands down as far as the "best" of those places. But...it really depends on you and what exactly you want. Cambridge is awesome, cool people, "crunchy" community, urban, exciting, good public transportation, etc. It is very, very pricey tho
Next, I'd pick the Portland area. If you can handle the colder temps than the other locations. The area is great and fun, a bit urban, and a crunchy open-minded commuinity all around. Close to lots of outdoor activities, etc. And cheaper than Boston.
I don't know enough about Northampton to help on that one. I have been to Western Mass plenty of times but not enough to give advice on it.
I have lived in NH (near ME side) and currently live near Providence. I came here to post this b/c I just can't post anymore negative things about RI for the sake of that tribe
The crunchy community is spread across the state w/ a few here and there. It's hard to connect compared to most places I have lived. The East Side is suppose to be crunchy but borderlines very close w/ pure snobbery. It is very expensive compared to the rest of Prov and keeps the community segregated b/c of a "if you can't afford it, you don't belong here" mentality, imo. The public transportation in RI is a joke. Straight up. The school system is doing even worse and some say that it is among the worst in the country! Homeschool laws are even worse (RI hits top 5 places NOT to HS in) and very rigid as it is not the norm. Crunchy is just not this state. It is corrupt and you see it all around you. It is hard to get around (but that can be said for all of New England, really) and it's just not very nice out here. There are places in RI that have pockets of "nice" but the crunchy part does not come along w/ it.
We have ONE midwife who will attend HB's from RI (a few others will cross over from CT and MA) b/c of the laws regarding CNM/CPM's. That said, we do need more HB MW's here for sure!
The positives for Prov are: cheaper rent depending on where you live (but, you get what you pay for, kwim?), at least they have the east side for those that can even afford it, and it's 3 hours from NYC if you have no traffic and arrive in the middle of the night
I just can't tell someone, anyone, to move to Prov. Ever. Especially when our goal (the minute we got here) was to leave!
I have also lived in Portland (OR) and Seattle, probably THE most open minded/"crunchiest" communities around, so I base crunchy off of them, and Prov ain't it! However, Portland (ME) and Cambridge are great choices (and fwiw, I have heard this to be true of Northampton).
good luck, I can't wait to see where you end up!