TPM is probably the most painful to sit through for me. When I watch AOTC & ROTS, for all of their problems (plot holes, dubious acting, flat direction, stiled dialogue) at least something is actually happening. Phantom Menace just reeks of padding and redundancy.
And god help me, at least with the latter two movies, I can see a hint of competent acting by Hayden even with the awful direction Lucas gives him. With Jake Lloyd, its just bad directing, on top of saccharine dialogue on top of a lousy child actor. When they converge for stuff like "Yipee" its just too much.