It would depend on which room you enjoy the most when sewing. More room is great as long as you are happy with the lighting, the color of the room and the amount of visitors you get in your sewing room. I would prefer a small bright room that has a happy color on the walls to a bigger, darker room that does not have a happy color on the walls. Also, does one room make you feel isolated from everyone more than another room. Do you want to have that isolated feeling?
Those are the questions I would be asking myself.