Well a dominant champion means beating your contenders to your crown. Hopkins, Hagler and Monzon did this, you look at who the top middles of their day were, and they beat them. The only way to separate them would be on small details. Like you could give the edge to Monzon for not ever losing his title, you could also give an edge to Hopkins in your own mind if you think he beat Taylor at least once. You could let Hagler off because the man he lost his championship to was not actually a middleweight contender. It all just depends on how you see it and judge it, i might lean towards Monzon. When all is said and done, a lot of Hopkins' defences were not of the lineal title, but he still should be credited for defending his alphabet titles with the air and dignity of a champion.
I might sound like a broken record but Carlos Monzon was the greatest middleweight champion AND had the most dominant title reign..the opposition he faced was greater than either Hopkins or Hagler plus...the big plus...he was NEVER BEATEN..retiring undefeated as champion pushes Monzon to the top.
Actually I change my stance...Hopkins actually lost during his reign, perhaps 2 of them were arguable, at the very least the first Taylor fight, but Monzon did not..Really no other way to look at it. Either way..it appears Nonpariel and Fitz are firming as the true correct choices for this thread.