The straight dope on neutering of male dogs is that the process of having them neutered actually increases their chances of suffering from certain types of cancers. Supposed increased life expectancy related to neutering is just related to the owners of neutered animals being more willing to invest in their animals. Attributing it to anatomy constitutes conflating correlation with causation. If you just isolate anatomy, the reality is really a lot different.
Publication earlier this year of a study that found higher incidences of certain cancers and musculoskeletal disorders
www.avma.org
I am pretty sure that a more controlled study that focused on the actual direct anatomical effects of neutering would find that, in the long run, their life expectancy is really similar. It is just impossible, under natural conditions, to control for owners that just can't afford or can't be assed to neuter their animals, but the Humane Society keeps pressing the idea that everyone should do it because, in spite of their name, they are basically a ruthless animal genocide operation. They are going to do anything they can to perpetuate their extermination program.
Besides that, here is what I can tell you about how it affects your relationship with your dog to leave your dog intact.
It is easier to board your dog if your dog is neutered. Most pet boarding will not take an intact dog. There are also many dog parks that do not allow intact dogs into the park. You can get around this by simply hiring a pet-sitter instead of boarding: this can be done inexpensively. There are plenty of dog-parks that do allow intact dogs, and even if there is not one near you, there are plenty of mixed parks that welcome both humans and dogs.
Besides that, you can expect an intact male dog to act like any human in a similar condition: they act like men, first and foremost, and that's about the size of it. That comes with both positives and negatives:
European researchers examined the social behaviors of neutered versus intact dogs. Here’s what they found.
www.americanveterinarian.com
The intact dog is actually more socially outdoing and more likely to make friends with other dogs. It's ironic, since you would expect the opposite, for the intact dog to be antisocial and really aggressive toward other dogs, but apparently, it comes out as "manly charm" and "schmoozing" behavior instead. An intact dog wants to "be a big wheel." They are less fearful, and this actually translates into LESS behavioral problems: like with humans, fear is really the cause of most problems you have with them. There are your main advantages of an intact dog.
However, they are still men. They are hard-headed. They have their own ideas about how to do things. They also stay distracted most of the time because they quite frankly have dick on the brain. Like with men, they go through a stage in life where they want to literally fuck everything in sight, but this can be attenuated by just raising them right: they ultimately grow out of it.
Now, that's just my translation of what the study says, not what's true for every dog.
Anyway, your dog will live the longest EXACTLY if you give your dog routine veterinary care and feed your dog an appropriate balanced diet, not anything fancy, especially nothing exotic, no stupid "raw meat" diets (those can make your dog seriously sick), but mainstream zoophile recommended brand name foods are really your best bet.
That's the best information I have for you.
