From my point of view they are all great films, but I certainly understand the reverence saved for the first film. Very hard to say which is the better of the two sequels, mostly because they are so diametrically opposed in terms of how they are structured. So much of the genius of the third is how much the tables have turned and how Doc is acting on his emotions and Marty is the more logical one, while never seeming to betray the cores of each character. The way it plays with scene structures from the first, applied to the vastly different setting of the wild west, and that the film is essentially much more of a love story when it gets to the stuff with Mary Steenburgen's character.
I watched all three in their newest 4K restorations, which is a little bit fitting because I'm now living where I grew up, when I watched all three I don't know how many times. They all stand up in their own ways, to this day.