I've lived in New England (CT and MA) my entire life (I'm 23). I've lived in the city (Boston) and in the suburbs (Guilford - a shoreline town near New Haven). I'm a musician, writer and a startup guy so I have friends and relationships in a variety of circles.
I'd say that the best way to experience the friendliest cities is by being a respectful and inquisitive outsider.
On this tour I've done very little prior research before arriving in any town outside of planning each day of travel to be 5 hours or less. I wanted to intentionally go in with no expectations outside of what people on the road have told me.
Everywhere I've gone I have managed to connect with complete strangers that have become friends. I think the best thing you can do as a foreigner in a city (I consider myself a foreigner even though I'm a United States citizen) is to be open to whatever comes at you. Opting to sit with two strangers that asked if I wanted to join them at a seafood spot in Shreveport, LA resulted in me hanging out with them all day learning about the city, local politics, craft beer, wildlife conservation/fracking and more. I could have just said, "no thanks" and I would have wandered around town by myself all day.
So this is a bit of a ramble but I guess the point is that I set out on this tour thinking I'd move to Austin afterwards. I still think I will but every place I've passed through so far other than Baltimore (far too violent) has been a place I would consider living - at least for a few months to try it out. The best way to find a "friendly city" which by your definition just seems to be one that you like the people in, is to travel all around and see what resonates.
Happy to tell you more about my travels. julian at bundio.com