I've worked in at a vet clinic 4 years and at an animal shelter for 20 years. Been a full time "dog nut", since I was 14 and am now 51. I'm pretty up on all the various controversies concerning companion animals, since I am writing a book on it (I've authored 3 already).
There IS controversy about early age altering.
As a shelter worker, I push for early age altering (8 weeks and older) as I know that: a) the animal will only be a "pet" and never a serious working/sport animal. b) while scads of great people come to shelters to adopt, so do double scads of impulse buyers and those looking for cheap dogs with which to create those expensive "designer breeds". I would MUCH rather get the altering done with rescue and shelter dogs, and any physical issues will be of minimal consequence to a dog who is going to lead a pretty soft life activity wise.
As a working/sport dog freak, I absolutely WILL NOT alter my male dogs before 12 months of age. I have not found there to be a significant issue with the grump, and will spay as early as 8 months on them.
There is plenty of good info to be googled on the structural issues caused to male dogs by early altering. As well, I can EASILY pick out an "early age neuter" animal of my breed on sight. They look like labs in body type.
My recommendation is this: if you are the type who will "have an oops" experience because you didn't realize your grump was in heat (often difficult with coated breeds and on all breeds with first heats) then by all means get it done around 6 months of age.
If you are going to use your dog for any work/sport that requires real activity then wait on the males.
As well, I can tell you that the "myth" of behavior changes with altering is just that. Altering a male reduces SEX drive. It does not reduce HUNTING/PREY drive, DEFENSE drive, etc. It just takes away the crazyness when a female is in heat, making it kinder for dogs which are not going to be allowed to mate. IT DOES NOT STOP FIGHTING. It does not stop leg lifting in many cases - unless done young. It DOES REDUCE WANDERING - but ONLY with dogs that wandered due to looking for grump in heat. ALL dogs wander if not fenced, so altering a pup will NOT KEEP IT OUT OF THE ROAD!
Adult dogs which are altered can and will still mate with in heat females, they just won't be as avid about it.
Is a neutered dog much different from an unaltered dog? Yes and no. It depends on age. If you wait until your dog is mature, say altering after 16 months, your dog will change very, very little when altered. He may become a slightly better working or sport dog, with his mind on you more.
However, I have found that there are a number of woman (many who work in the animal welfare world) that are honest to gawd she-woman man-haters. They seem to hate ALL THINGS MALE. I had a friend like this in pit bull rescue once, who now, sadly, works for the organization, and she couldn't stand to even HEAR the word penis, or testicle, or anything. It seemed her mission in life was to round up every male animal on earth and take away its maleness. These folks are often in control of policy making, and explains the current hysteria over altering. Lord knows, no one knows there are too many unwanted dogs on this planet as much as I DO! I had to hold them in my arms and euthanise them (up to 10 a day) for 20 years. But I also believe that altering is a PERSONAL choice for the pet owner, and that those who keep whole animals, when they are not negatively impacting the community, should not be penalized by outrageous license fees, etc.
So there you go! Pups are cute.