Southbridge has some small city amenities and problems. There are good restaurants, and shops right in town. Houses are cheap but you will have a hard time selling it when you are ready to leave. Unfortunately the schools are not very good so I would be reluctant to raise a family there.
If you are single, MUST be in this part of MA, and willing to rent; I would choose Southbridge. If you have a family moving with you or must own; choose Charlton, Sturbridge, or, Auburn.