I'll only talk about the ones I know!
2.Lexington - haven't lived there, but similar in a lot of respects to the town I live in. I love Lexington, it's expensive but a great school systems, family friendly, low crime...downside - not very diverse.
3. Arlington - also haven't lived here, but similar to Lexington, the school system might be a step down or two though. Slightly more diverse than Arlington but not by much. Pretty low crime rate, not as expensive as Lexington.
4. Watertown - the cheaper of these three. I lived here for 10 years, and when we decided to buy we took Watertown off the table. My daughter was in the school system from k-4, I thought the teachers were great but was unimpressed with the school board and the middle school wasn't exactly doing it for me. Her elementary school was great, but I wasn't happy with the programs in either the middle or high school.
Watertown is very family friendly. The have the Watertown Family Network which hosts all sorts of stuff for the 5 and under set with moms/dads - sing-alongs, trick or treating at the elderly assisted living facility, yoga classes, things like that. They face budget issues every year but so far they've managed to remain viable.
The library is great, we still go one town over to hit up their library because it's so much better than ours (the kid's section, anyway). There are playgrounds everywhere. It's more diverse than Arlington or Lexington. The crime rate is higher than the other two towns, but not enough that it was a factor in our deciding to move. The school system was really what it boiled down to for us.
Em, married to Alex, mom to Samantha (11 yrs) and Cullen (5yrs) and Maybe (5/16/2010) Trying to grow 4,000lbs of produce on .2 acres. See my blog!