I personally think that Episode I is probably the most well constructed of the prequels solely (and I mean solely) because it starts from a straightforward premise and follows through with that premise effectively. I will not give it high praise, but it at least sees its story through to the end with minimal issues. The intricacies of the romantic entanglements and overblown politics of the latter prequels aren’t as fleshed out and thus cannot be as thoroughly effed-up as they will be in the later films. Episode I’s narrative structure is not fancy. it’s not good, but it’s not bad. It suffers, as all the prequels do, from poor dialogue and bland acting, and uniquely suffers from the most screentime allotted to Jar Jar, but on the whole, it’s a decent film. It also has the most satisfying climax and ending of the three. We get the fight with Maul, Obi-Wan’s coming-of-age, the passing of the torch from Qui-Gon to Obi-Wan, and the foreshadowing with Anakin. All very enjoyable, with a nice combination of closure and cliffhanger wrapped up in a bow. Also, added bonus, while little Anakin may be bratty and annoying, he is at least not perpetually horny and angsty, which I see as a definite plus.
Episode III is somewhat better constructed, but it absolutely falls apart at the end. As I told a friend, Episode III is tolerable for most of its running time, and absolutely tanks at the end (after Anakin turns to the dark side). Episode III has a very fatalistic feel to it, but in a good way. You as the audience sort of know what’s coming, and you know that Anakin’s going to go bad in some way. But then he does go bad, but like... at the drop of a hat. There’s no real build up, no satisfying motivation for him to do so. They absolutely hamstring Padme’s character to give Anakin the Man Pain™ needed to justify his turn to the dark, but it’s just not enough to suspend my disbelief. I’m just left with a disappointed feeling in both Anakin and Padme. (Lost the will to live? LOST THE WILL TO LIVE???) The fight between Obi-Wan and Anakin is pretty fun to watch, but the pacing (particularly at the end) is really wonky and not all the scenes make sense. It’s WORLDS better than Episode II, but not quite as unoffensive as Episode I. And that’s the main difference between I and III. I is not good. It’s just very unoffensive, because it is quite simple in structure. Episode III has a lot more moving parts, a lot more subplots, and a lot higher emotional stakes, which gives it a lot more to screw up. And unfortunately for III, it screws up most of its narrative promises to the viewer and ends with a fizzle. Some of its struggles are holdovers from II, such as the sexism shown towards Padme. Another example is its bungling of the complicated Jedi/Senate politics, which I’m very bitter about because it could have been so good. Politics is also something that could have been interesting that Episode I made exceptionally boring, but in Episode I, politics was a plot device. In Episode III, politics are a character device, which makes their bungling all the more catastrophic to the quality of the movie. There’s a lot in Episode III that could have been amazing, but wasn’t. And perhaps that is the deciding factor for me to rank I above III. Episode I had a (fairly) low bar in terms of plot and construction. It was a simple premise and a simple execution. There were problems, but overall, it is enjoyable. But III set its ambitions so high, that when it failed to deliver on those ambitions, even if it has more interesting ideas than I, the viewer still leaves with a more disappointed taste in their mouth.
Meanwhile, Episode II is just... bad. It’s just bad, okay? The romance is bad, Anakin’s motivations are bad, bad writing, bad dialog, bad pacing, bad mullets, it’s just... it’s just bad. They made Sir Christopher Lee look bad. SIR CHRISTOPHER LEE. Add to that the CGI that has NOT aged well and the absolutely abominable sexism and male-gaze corniness that was thrust upon poor Padme, and it’s just... nothing about it is good. I hate it.