Jar-Jar… For sure !!! Can’t think about a worst character in the whole saga…
You might think so on face value but Jar-Jar (largely) isn’t in AOTC and ROTS and many people seem to “prefer” TPM to those two.
Perhaps it’s (PT) Anakin?
If he had been a heroic, charming, sexy, dashing, clever, skillful, funny, loveable, exciting etc etc character who was central to, and the focus off, the plot*… I bet many of us here would almost have forgiven 99% of the other cr*p in the prequels.
(* Like, for example, Rey)