Just pick a jetty before 10 am and after 5pm (lifeguards) if you want to have a pleasurable experience surfing NJ that time of year, wherever you end up. The better known spots will be mobbed if there's a decent wave, and the next jetty down might be just as good. That time of year is usually feast or famine, and if there's tropical swell, usually (not always) every town gets their share so take your pick. Have fun and play nice.
In August in NJ it mostly depends on whether there's a hurricane moving up the coast and how the wind is blowing. I've had tons of times where this website along with others said it would only be 2-3ft, when really it's around 4-6ft because of a northern wind. This may only be my beach, but when the wind is blowing from the north, the waves get much larger and develop huge barrels.