I vote ROTS as the worst prequel. Hayden ranting and the horribly overacted emperor, the Mustafart battle and the Yoda/Palpatine fight, plus Padme being reduced to a total nothing, all topped off with "Noooooo!!"
But AOTC is pretty rotten. It's just not as extreme as ROTS. Those two films are way worse than TPM. TPM actually has some charm, just not when compared to the OT films. AOTC and ROTS are total dogshite and have some of the lamest stuff in cinema history. "You underestimate my POWER!!!" "I hate you!!!"
The Yoda/Dooku fight is idiotic. Yoda buzzing around, flitting around, like a big glowing bug. And Dooku also comes off so full of himself. The arena battle was pathetic. All this big spectacle with all these Jedi and it was done so feelinglessly. I totally fail to see the point of that droid factory obstacle course nonsense. I did like the Kenobi/Jango fight, though. It had atmosphere and, unlike most of these two films, it was actually involving. The flying car chase at the beginning wasn't bad either.
The romance in AOTC is of course bad news. That goes without saying. And Padme seems to find Anakin charming even when he's talking like a psycho or admitting he's murdered a whole tribe. Hayden Christensen's performance is painful. I mean, THIS is the Anakin we waited all these years to see?