Lots of the ideal dog thing depends on what traits you'd value and hate
The dogs mentioned on this thread are someone's dream and someone else's nightmare.
This is especially important if there is an expectation of a bond with someone who has autism because they tend to find it harder to forgive. A golden for example will likely go through a bouncy period, and a chewing period so it will depend on if your DC is able to bond with a dog who also knocks them and their prized possessions over. They do tend to calm down after around 2.5 years but that's a long time to wait if the adolescence stage is hard
A Bassett is a personal favourite but stubborn as hell, and id not recommend to anyone noise sensitive. Poodles are really clever, amazing if dc wants to teach tricks, less so if you want a dog that isnt intense. Labs are foody, but also likely to mug you for food. All breeds will vary in their degree of biting and mouthing
Lots of these can be trained out, but will be present for a significant period, and possibly life (eg noise levels).
We used to see a lot of dogs in rescue bought for neurodiverse children where a big rift had formed and they couldnt wait for adult dog calmness or recover their trust. Its really hard when this dog is a thing that forces you out into the rain, ate your favourite toy, pushes you over, bites your hands, barks a lot, scratches your legs when they jump up and destroys your lego set up.
Its worth thinking about what you want from a dog and what you would hate. A play friend or a snuggle buddy? How much time can you walk it? How long will it be left? You dont have to tell me but its worth having an idea of what your perfect dog behaves like
Id recommend considering an adult dog to anyone with children. Simply because trying not to overhype a puppy (which makes them bitey) is really hard in a busy household with kids