If Montessori is the one best treatment, I would have been a miserable failure. I work best when I do have structure.
For example, I love reading. (Could read before I spoke, actually.) I have a large vocabulary and an instinctive grasp of grammar because of this.
It wasn't until I was actually forced to write, in great amounts, as part of an AP English course, that I really learned how to write. (And, am severely out of practice, alas.)
Montessori, if I remember right, would allow me to read, but not force me to write. And the majority of people I've met with AD(H)D- screw it, hyperactivity- would love to be in an environment that allowed them to do what they like, but would never force them to do other things. I don't know anybody my age with hyperactivity who didn't succeed without a process of careful attention to force them to learn how to do various things until it became a habit.
So, in a nutshell: how exactly is Montessori the best option?

I too have a mild case of it, and have been diagnosed for... 37 years? Something like that.
From my standpoint, it's not just sitting down, it's practicing the sitting down, forcing myself to do it, until it becomes a learned instinctive behavior.

Credentials: ADD from back when it was hyperactivity. Been on the Feingold Diet (worked for me, not for everybody), various drugs (works for me, not for everybody), and a lot of forced practice courtesy of mom (would probably work on everybody, since she's a force of nature).

I"ve heard various things about this, over the years, and the question that occurs to me: what happens when they've re-trained the brain this way, to the *good* aspects of ADHD?

I can zip through solving problems in a way that a lot of other people can't. I can 'see' the solution when working at fixing something mechanical. I can also spot discrepancies - visual, aural, logical - much quicker than my friends.

How much of this goes away? That would be a very interesting followup research project, IMHO.