Haverhill vs. Northampton is a no brainer. Haverhill unfortunately is heading in a not great direction these days.

Westbrook, ME has a super walkable downtown. It's not a "cute" downtown and the park gets a bit methy, but it's not like there are homeless camps there. Good beer there at Mast Landing.

Brunswick is great college town with a great walkable downtown. Traffic there in the summer is tough if you are trying to do something away from Bowdoin - other than that it's a great option.