I think TOS is Roddenberry's actual vision before he bought into the hype that he was changing the world and before his mental faculties began to deteriorate.
Sure, we can get into details like whether TNG is more utopian than TOS and which vision is better. I'd say they all have their advantages and disadvantages, I enjoy TNG's at its most utopian as much as DS9 during its darkest hours.
I merely wanted to say that is the common denominator of all Trek incarnations is that it features a better future. Just like 1984 or Blade Runner features a worse future and Firefly features a future that is basically like the present.