Castration of your dog may not necessarily affect the behavior of your dog. But on a professional advice I prefer the dog to be a little mature to allow him have some testosterone. On interest is a case I participated some years back: We were suppose to castrate a Zoo Lion but the Zoo veterinarian suggested that Lions should be vasectomized since if castrated they would lose their wild demeanor. I Here are some photos
I'm not a veterinarian, but being in the veterinary field for 15 years, I've seen some things. With Pit Bulls especially, I've noticed that you can certainly tell when you have an un-neutered male. Their muscular stature is more developed than in a neutered male. Same thing goes for cats. Male cats that aren't neutered develop a larger head due to the testosterone. Not sure what the vets would say about it, but I've seen the difference.