All have memorable songs in them, except TFA and R1. Not sure if I could rank them, although some are better than others, so I'll just post my favorite songs here. In no order:
"Duel of the Fates" (TPM) - https://m.youtube.com/watch?v=qzVBqBosf5w
"Across the Stars" (AotC) - https://m.youtube.com/watch?v=jFcuT4Nbcb8
"March at the Jedi Temple" (RotS) - https://m.youtube.com/watch?v=iqK8h9psLCs
"Anakin's Dark Deeds" (RotS) - https://m.youtube.com/watch?v=NxLlnyLa7Xo
"Battle of Heroes" (RotS) - https://m.youtube.com/watch?v=FHuD5y-PZM0
"Padme's Funeral" (RotS) - https://m.youtube.com/watch?v=m3KpEMyl-oY
"Main Theme" (ANH) - https://m.youtube.com/watch?v=fl7MI8ZlczE
"Binary Sunset" (ANH) - https://m.youtube.com/watch?v=fl7MI8ZlczE
"Cantina Band" (ANH) - https://m.youtube.com/watch?v=bAxokC7vvjQ
"Throne Room" (ANH) - https://m.youtube.com/watch?v=BjDaPOWdx6s
"End Title" (ANH) - https://m.youtube.com/watch?v=sIPNormrPwg
"Imperial March" (ESB) - https://m.youtube.com/watch?v=-bzWSJG93P8
"The Force Theme" (ESB) - https://m.youtube.com/watch?v=HMUKGTkiWik
"Han Solo and the Princess" (ESB) - https://m.youtube.com/watch?v=HMUKGTkiWik
"The Emperor's Throne Room" (RotJ) - https://m.youtube.com/watch?v=8H26Hdv3i0U
"Luke vs Vader (dunno it's actual name but whatever)" (RotJ) - https://m.youtube.com/watch?v=L63In39n86c
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Overall, maybe RotS had the best, followed by the OT and finally the rest of PT. The new films are rock bottom though.
Damn why do you have to make it so difficult? It's all John Williams after all (except R1).
I'd say in no real order:
Battle of Endor 2
Duel of the heroes
Catina Band numbers one and two
Intro theme (of course)
Jabba's baroque recital
AotC Confrontation with Count Dooku and Finale
Across the stars
Jedi Temple march (CIS theme)
Duel of the Fates
The throne room
Leia's theme
Asteroid field
Emperor's theme
Padme's funeral
Honestly too many to list...many of these track carried hard to compensate for the shittiness of the prequels no joke.
Honorable mentions from TCW:
Mandalorians of Death Watch Theme
The soundtrack that plays with many of the fights during season 4,5,6 (Maul vs Vizsla, sheev vs yoda + anakin)
Ahsoka's theme when she leaves
Edit:
Let me add on Lando's Palace to the main list as well as the Ewok Theme
and
the Battle of Hoth
and
Snow Speeder Rescue
Imperial theme has been overused in everything that it's hard to even think of it without being annoyed. Williams really is legendary.
I found this really cool playlist if anyone is interested of the OT tracks made into jazz pieces. Really good.
https://www.youtube.com/playlist?list=PLD20F0D1FEB1A8B84
The best soundtracks are ROTS and ANH. I love every song they produced in those.
TPM and AotC were mostly mediocre, but that's made up for via Duel of the Fates and Across the Stars.
ESB and ROTJ were great all-around, producing the classic love theme, Vader's theme and the final fight.
I loved the initial Kylo Ren theme in TFA. Rey's theme was also an instant classic. R1 had the Vader final fight.
My favorite theme of all is either the Victory Celebration from ROTJ or Across the Stars from AOTC.
I wouldn't call any of William's soundtracks mediocre. TPM had quite a few other great new tracks such as the Trade Federation theme or the Flag Parade (which play before the podrace). AotC, which is easily Williams weakest both in terms of new themes and reusing old ones, also creates the theme that play during the Jedi Temple March though it does not appear in the film but rather only on the soundtrack (the track is called the Arena).