Hi Mary--that is a big question--depends on what is important to you. Petaluma and Sonoma are both closer to San Francisco commute areas. Sonoma has a wonderful, if touristy, main plaza with the historical old mission and some fabulous homes. Petaluma is more of a working town, with a downtown area of live work lofts and a vibrant restaurant community. Santa Rosa is the largest town of all but has many quaint residential districts with varying architecture. Petaluma is cooler and windier, as is the south end of Sonoma. What the pluses and minuses are probably depends on your viewpoint and interests. I imagine we could have the same conversation about Lake Oswego, Beaverton and Portland! ;) Perhaps you can explain your interests a bit further.