When I first saw the revised version of the duel when it came out last year I was completely wowed. It took a lot of the context of lightsaber dueling that was established in the PT and put it into the first lightsaber duel we ever saw.
As I re-watched it today? I couldn't help but notice how different the new scene was from a cinematic standpoint to all of the legacy scenes that surrounded it. The camera moves were remarkably different, as was the lighting and cinematography. In this respect it takes me out of the duel because I'm noticing how different it is from the shots of Han, Luke, Leia and Chewbacca instead of just focusing on the story of the duel. In this respect I think the Adywan version fits in better with the surrounding shots, and there's much more of a sense of visual continuity.
And then there's the production issues / story / in universe explanations. Word has it that both David Prowse and Alec Guiness were not very adept as duelists. From what I understand it was hard for Prowse to see in the helmet. And the lightsabers that were used on set were fragile, with the blades actually made of a coated glass that would reflect to be used for the special effects. They couldn't touch blades otherwise they might shatter. And I know that in TESB and ROTJ Prowse didn't do the dueling. I suspect that there was disappointment with Prowse's dueling abilities in the first movie, and that is almost certainly why he was replaced in the lightsaber dueling scenes by swordmaster Bob Anderson for the rest of the OT. Anderson trained Mark Hamill as well, and was far more capable than David Prowse as a duelist. He might have improved the style of duel we saw in ANH, but we'll never know.
What I recall hearing George Lucas say was that both Vader and Obi-Wan had not dueled in any significant capacity in years. All of the Jedi had been hunted down by Vader years before, and his dueling skills had declined. Another explanation that I've seen people offer was that Vader was defensive too, thinking back to how gravely wounded he was on Mustafar (although this is coming from a pure retcon standpoint). And Obi-Wan's skills had become far more defensive in nature, but also more strategically measured - see the way he dueled Maul in REBELS. During the duel Vader said to Obi-Wan "Your powers are weak, old man". That's something of an indication in the scene that Obi-Wan is either past his prime or holding back. There's also the theory that he was stalling for time so that Luke, Leia and the crew could escape on the Millennium Falcon - this is a pretty clear story motivation that I think would date back to the original realization of the duel.
I think the one REALLY BIG wrench that gets thrown in the works related to the ANH duel is Vader's massacre of the Rebel troopers on the Profundity in ROGUE ONE. He sliced through them as if they weren't there. And that scene blew the minds of the audience. But looking through that sequence? Vader's movements seem reasonably consistent with how we see him in ANH. He relied very heavily on Force abilities to block the blaster shots, along with throwing the troopers around and pulling away their blasters. And when he started slashing them with the lightsaber the movements seemed reminiscent of OT Vader. But physically he lumbers down the hall. He isn't quick at all as he moves, and is only quick as he moves the saber to deflect the blaster bolts. He's deliberate. He relied on terror and using the Dark side.
Watching the saga in episodic order I can completely appreciate how out of place the original ANH duel is in relation to other duels - especially considering how the duel in TPM and the Obi-Wan vs Anakin duel in ROTS raised the stakes. It makes me think of something that George Lucas said about the OT, the special editions and the PT - "Movies are never finished, they're abandoned". Meaning that he always had things that he wanted to make better in his films, but because of time / budget or other considerations there's a degree of settling for what filmmakers can achieve, and nothing can truly be a perfect realization of the filmmaker's vision.