I recommend Urban Adventours for local tours and bike rentals in Boston. I refer visitors there and they always come back happy. If you are going to Boston, it's much better than using the Hubway. They have GREAT bikes, high quality Konas with disc brakes. They are well-marked with reflectors.
Boston is a good city to bike around because it's so compact, and UA does a really nice job facilitating tours.
They also have a great small shop, they do a great job on repairs.