I think it is bit premature for Massachusetts to have such a category :) MA needs to invest more $$ in public awareness and stimulus for building "green". We don't even have an easy way for contractors to find and buy building products that are non-toxic, environmentally friendly, sustainable, etc.
If you want to compile a list, you may want to start with a bit more specific term than "greenest" (this one is not well understood and still requires a lot of education to comprehend for most). You may want to start with the list of, lets say, the towns that are "fossil fuel friendly" or "have cleaner air" or "alternative energy champions", and such.
In any case, I'll be curious to see what you came up with, Tim. Good luck.