Well here's how things stack up for me, very crudely summed up, why I fell in love with each film.
ROTJ
-First time we saw a green lightsaber
-Luke's best wardrobe in the trilogy (my opinion)
-First seeing the intricate workings of Vader's helmet
-The Emperor
-The most heavily involved space battle of the trilogy
-Speeder bikes
-New, fun creatures in the Ewoks (say what you want about them now, but to a 4 year old they were cool)
-The revealing of what lay beneath Darth Vader's helmet
-John Williams score to Luke's final confrontation with Vader and Luke being Sith Lightninged to death and saved by his father.
-Jabba the Hutt and his palace menagerie
-The Rancor
-The union of 3 Jedi friends in the spirit world
-The fun Ewok celebration song (pre Special Editions)
-Han Solo in Carbonite and coming out of it
-Leia as Boussh (always enjoying seeing characters out of their element)
-Princess Leia looking beautiful in her slave girl outfit
ROTS
-A thrilling space battle (while not the ROTJ battle it was originally set to be before editing, I think it was a visually fun ride with the pans and dives of Anakin and Obi-Wan's fighters.)
-Anakin's wardrobe and hair (loved the scar, the gauntlet was very cool, the darker Jedi robes were nice too, and even the hair I liked)
-Ewan McGreggor's fantastic final portrayal of Obi-Wan Kenobi, giving us the noble, awe-inspiring Jedi Knight the OT left us to think he once was
-The amazing design of General Grievous giving us another unique and visually appealling character
-The new Jedi Starfighters, great looking ships, probably my favorite one-man vehicles of the saga
-Ian McDiarmid's amazing performance as Palpatine, he always brought an A game to each film, but he really shined his talents in this film
-Mace vs Palpatine lightsaber duel
-Diverse clonetroopers (I like stormtroopers and AOTC clones, but these guys really ranged in armor and all and had some amazing designs, Commander Cody my favorite of all)
-Seeing the legendary eradication of the Jedi Order
-Natalie Portman making pregnancy look sexy
-Mustafar, a wonderfully pieced together world that looked splendid every second it was in frame
-Yoda vs Sidious in the Coruscant Senate Chamber
-The bridges to the OT, such as the reappearance of Tantive IV
-The construction of Anakin Skywalker's body into Darth Vader
-Seeing the early stages of the Death Star's construction
-A great score from John Williams, especially all of the music used for Anakin and Obi-Wan's duel
-And last but not least, Anakin vs. Obi-Wan, the duel we dreamt of seeing for years since merchandising told of how Vader came to be, and the most amazing lightsaber duel of the saga, and ya, Maul lover is ranking this one over the Maul duel