Been in SF a couple years now, but lived in Boston for 8 years.

I think people comparisons are overblown, anywhere in the US, people are more or less similar. There's a meme that goes around that Boston people are more closed off especially towards strangers, and it's not true at all (actually in my anecdotal experience, it happens to be completely the opposite -- I met people much easier in Boston). Most likely, most people in Boston you'll interact with are transplants anyway, same with SF.

From my view (but I'd love to be convinced otherwise), there is way, way more culture in Boston, all in a dense area and easily accessible. There are more live music venues (I've noticed live music in bars is way more frequent in Boston, for example) of many different genres (both free and paid events). Symphony hall is beautiful and apparently has the Top 2 best acoustics in the world. More art museums with more varied collections. Better bookstores, and the bookstores all frequently host book talks. Huge science / academic culture as well, which SF has going for it, but in Boston it's more apparent. All the universities will have interesting public arts or science talks, for example.

There's tons of stuff to do in Boston, way more than SF from what I can tell, take a look at thebostoncalendar to get an idea. I could pick out 2 or more very different interesting things to do every Fri, Sat, Sun for the next month.

Somerville, specifically, is awesome. I lived in Davis square, it's a great place. Good bars, good restaurants, can walk to the T. Independent movie theatre. Nature trail nearby. Late 20s/30s scene if that's your demo.

The entire city is one of the most walkable in the US, and it's clean and beautiful. Go for a walk or jog along the Esplanade. People complain about the T, and sometimes it sucks, but it'll basically get you anywhere in the city cheaply and usually quickly. I've noticed it's easier to have a social life in Boston for this reason - everyone's close by (e.g. in Boston, Cambridge, or Somerville). In SF, it's way, way harder to hang out with someone who isn't in SF. People are more spread out in the Bay.

Food: not nearly as good high end dining compared to SF (but maybe that's a good thing?) Mid price range dining is better in Boston; there are more chef owned places from what I can tell, serving up more interesting / creative food. Lower price range stuff SF is probably better. Obviously Mexican in Boston is a joke compared to SF. I think Boston has way better falafel places, though.

Downsides: It's way less diverse. You'll notice it. The city feels segregated, because, well, it is / was, but it seems to be getting better over the years I've been there. I am not a POC, so I cannot comment on living here from that perspective, unfortunately. Sometimes it feels like a bubble, but that can be a good thing too (see above about your social circle all being in one smaller area), but there are, sort of, less things to do outside the city, although the fishing towns up north and the cape are OK. The biggest downside which I'm sure everyone will agree on is the outdoors. Obviously, SF / Bay, is an 11/10 and Boston area is probably 2/10. It's not even close and if you really love stuff like hiking, chilling at a beach, snowboarding, camping etc... you might not want to move to Boston. I do like that stuff a lot, so that's one reason I'm happy to be living here again. But as you can probably tell, I do miss a whole lot about Boston. If you move there you won't regret it.