Which Star Wars prequel do YOU (yes, YOU!) think had the strongest dialogue?

[Yukaphile]

"I have failed you, Anakin. I have failed you."
"I should've known the Jedi were plotting to take over!"
"Anakin, Chancellor Palpatine is evil!"
"From my point of view, the Jedi are evil!"
"WELL THEN YOU ARE LOST!"

Seriously, that's... really cheesy, over-the-top, and just... ugh. It's not the Vader we all knew in the original trilogy. It's just... ham and cheese, baked into lemon.

[Elderdog]

The visuals helped. Otherwise, I would say that the acting elevated the dialogue above what it could have been under the circumstances; Ewan McGregor especially killed it in this scene with his body language and delivery. Sure the dialogue was "tell" rather than "show", but it served its purpose to portray the genuine tragedy of the final battle. Obi-Wan is desperately trying to find a way to save his friend only to slowly realize that it's to late and Anakin has given into the Dark side so much that he's lost himself.
On an unrelated note- From a certain point of view (I know it's a cliche) I would argue that what we're getting is the raw Vader rather than the cold calculating monster that he would become, could it have been done better? Yes, but I can forgive the personality shift considering that the Dark side, when distilled down to it's most basic form is irrational. After all didn't Yoda say "Fear leads to anger. Anger leads to hate. Hate leads to suffering." and what better illustrates that saying more than this scene?
Tl;DR: The acting and visuals help, the dialogue is serviceable and Yoda was right.

[Yukaphile]

And that's another way the prequels fail. Fear doesn't always lead to anger.

[Mecha82]

Pretty much. After all it's clear that way he was in RotS and in that duel with his former master and former friend was different than he would eventually become during time between ending of RotS and beginning of ANH (and Rogue One). His time as Palpatine's apprentice did effect him as well as all pain that he was in and hate and anger resulting from that that he learned to use as source of power. It's easy to even those that don't know about those events from novels and comic books to realize that because it makes sense.