I refer to the East side of Petaluma as offering the "cul-de-sac" lifestyle. It has the safety of quiet streets for kids to play in and a very friendly suburban California feel. It is the newer side of town as most of the developers began expanding eastward into the formerly industrial/farming area in the 60s and 70s. The neighborhood around La Tercera has a lot of longtime/original owners and many newer buyers who have recently benefitted from the purchase of distressed and flipped homes in the neighborhood.
In my opinion, the attitudes about West v. East side are very subjective. It depends on what you are looking for. The West side has the charming old Victorians and proximity to downtown restaurants, live entertainment and street fairs, all of which are very accessible by bike, car, bus or taxi from the East side.
The all-around appeal of Petaluma is its small-town charm (most recently highlighted in the hometown pride and excitement surrounding our Little League's success) and the fact that we are located within such a short distance of incredible places such as the beach, San Francisco, Tahoe and many others.
This town offers, in general, such a wonderful quality of life. In the coming months we look forward to the Pumpkin patches opening up. During Halloween, the Downtown Association puts on "Trick-or-treat Trail" with most of the downtown businesses opening up for the younger treat seekers.
I am definitely biased, but I couldn't imagine a better, more family-friendly place to live. I hope this has helped you.