There are so many things wrong with the prequels-as to tie them up with the originals, but if I had to choose its Episode 3.
There were a few things I liked about Episode 1, the pod race, the duel and Darth Maul :P but the rest of it, was too much like a kid movie and then got really complicated and confusing in the politcial part of it.
And I haven't been able to even force myself to watch Episode 2. It's just really bad to me, in the story and most of the scenes between anakin and padme are so embarrassing.
The fight between Obi-Wan and Grevious was a joke and anakin's whinning really frustrates and annoys me, but like I said, if I had to choose E3.
~I'm just a SciFi Geek with way too much time on her hands~