I don't have a link for it, but I've read an interview with Mark Hamill in which he stated he was going to see the movie after it came out, when he got a call from Lucas asking him to come in and dub more lines for the mono mix, which hadn't been completed yet. This would give further credence to reports of the mono version not coming out until after the others.
I have to wonder if those re-recorded lines have since been lost, since they never appeared on any later mixes other than the mono. Or perhaps it was simply a 'creative' decision to retain the originals.
I'm pretty sure the 35mm stereo came out first, followed closely by the 70mm. The 70 is nearly identical to the 35, but it does have a few added sound effects, namely the screeching sound when Vader destroys the first Y-wing in the trench, and a loud explosion when the Falcon saves the day by destroying the first of Vader's wingmen. Other than that, the main difference between the two is from the vastly superior dynamics and bass content of the 70, which are at least partially represented by the '93 remix, and by having discrete channels.
The mono version is interesting. In some parts it really does sound more polished and complete than the stereo track--I particularly like the added 'deceleration' sound when the Falcon comes out of lightspeed, and the whining of stressed electronics when the ship is caught in the tractor beam. (Though obviously it is missing the strong bass of the 70mm version.) A subtle but cool change is that the beeping intercom in the cell bay shootout starts much earlier, while Luke and Han are still blasting away, showing that the people on the other end were very quick to respond to the disturbance in the detention block. The music throughout the movie is more audible and really pulls you into the excitement of the film. But some things they changed are definitely less good. The sound just before C-3PO says "Did you hear that? They shut down the main reactor. We'll be destroyed for sure," is for some reason very tinny and subdued in comparison to the stereo, and I don't like the alterations to stormtrooper dialogue such as "close the blast doors", which are very obviously not the same voice, and distractingly unnecessary. The '44 Magnum laser' in the chasm shootout is questionable too.
Obviously, everyone's view of what mix is best will vary according to what they heard first and what they come to prefer through repeated listening. It's hard to pick out any single one as being superior in all aspects to the others. Each has their strong suits.