There is a lot of information here on neutering. Search is your friend. Most folks say don't expect a significant behavior change. If anything, neutered males are slightly more aggressive to non neutered males. Almost everyone agrees that it should be delayed until the dog is fully grown, to protect joint growth. It is more common in the US than in the UK, partly because license fees are lower for neutered dogs. Animal control makes the argument that it reduces unwanted dogs so they encourage it. Many owners spay females, just to avoid the possibility of unwanted pups. Not really an issue with males, though some (many) doggie daycares will not take an un-neutered dog over a year old.
Many Vets still pressure their clients to early neuter and spay but the prevailing thought is that the later the better for the long term heath of the animal. 18 months is the earliest a male should be neutered and a female should not be spayed until after her first heat with a wait of 3 months following that heat. If you want your dog to look like its unaltered parents, then you need to allow the dog to reach maturity and the end of growth for that to happen. If your male is an escape artist and you live where he will be exposed to intact females, then you have to factor that into your decision. CAN you ensure that your male will not escape and breed with an intact female down the street if her owners don't take the proper precautions to keep them from getting together? Or visa versa. After all is taken into consideration, you are the owner and the decision is up to you.
I haven't neutered either of my adult Labs, but I do keep threatening to every time I clean the walls and doors of the dried on willy drippings!
