To at least a small extent you can't compare the 3.x and 1E AD&D DMG's. The former was written after 25 years of advancement in RPG game theory, rpg playtesting with D&D and many other systems, etc. The latter, while perhaps written not while the game was still in it's infancy but certainly before it had yet reached maturity, is in so many ways a completely different work because it was not yet well-realized exactly what a DMG, or indeed ANY rpg book, could or should be much less the what the game itself could or should be. The elder DMG was written because there was SO MUCH STUFF that it was desired to impart to gamers it could not possibly fill one book. It took three books. And they weren't all written simultaneously as the 3E books largely were. With the 3E books they were publishing a comprehensive game system that was largely already complete (and TESTED) and were seeking to do it quickly and efficiently. With the 1E books it was a full year betwen the publication of the MM and the PH, then between the PH and DMG.
In trying to keep that in mind you cannot compare the actual game SYSTEM itself that each book uses. You can't compare the two DMG's and give the newer one an edge simply because the game system is in some way superior. Therefore comapring the two is a HEAVILY subjective excercise, much as any ordinary review would be subjective.
The 1E DMG was BADLY organized. But I never really faulted it for that. There was so much information covering so many subjects and no pattern for a previous book having done much the same thing to refer back to. It was all-new ground being broken and so as far as that goes I think it was at least adequate. The authors writing style is REPEATEDLY referred to by everyone who reads the original DMG. Regardless of the content of the book it cannot be denied that the large vocabulary and slightly archaic prose style of the author imparts an amazing amount of character to the game as a whole. I think it CAN be faulted for failing to adequately explain some rules that NEEDED a simpler, even simplistic[/] explanation and modern prose style as well as CONTRIBUTING to the disorganization of the material due to the authors tendency to drift from topic to topic rather than working to bring it together into a cohesive, organized whole.
But again, I hesitate to be overly critical in that area - it was the first RPG book of its kind. ALL books that came after it would be compared to IT, not IT to THEM. They would note it's mistakes and inadequacies and try not to repeat them. They would note it's achievements and strengths and try to copy them. If the author had known then what we know now it WOULD be the perfect RPG book. I'm not sure it could be given that title now - but it would be in the running.