I waited until 16 weeks to take him to my favorite dog park -- a place with lots of dogs. But I think it is important to socialize your puppy from the moment he leaves his mother and littermates. Going places and doing things and interacting with other people and dogs is important for the development of a stable happy temperament. So I tried to give my puppy a lot of interesting happy experiences, while protecting him from anything scary or dangerous. I took him to the houses of friends who have dogs, invited them to my house, and took him out in the car from the time he was about 9 weeks old. Starting at maybe 12 weeks (I forget exactly when), I walked around the neighborhood and took him to a park where a few neighbors walk their dogs and let them off lead. I know just about all the dogs that go there and am confident that they are up to date on immunizations.
This is certainly a controversial topic, but I am surprised to hear that you have found that breeders are advising waiting until 16 weeks. In my experience most breeders are aware of the need to socialize young puppies, but vets often focus only on preventing disease and not on the need to socialize. My vet initially recommended waiting until after the pup gets the 16 week shots, but when I asked more questions, he acknowledged that the risk of parvo was extremely small so long as I avoided dog parks and other places with high dog traffic.