Simple enough, it’s all John Williams for all six movies, so here are my favorite tracks from all six soundtracks.
The Asteroid Field (Empire)
The Return of the Jedi (duh)
Duel of the Fates (Phantom)
Anakin vs. Obi Wan (Sith)
Jango’s Escape (Clones)
The Imperial March (Empire)
The Emperor’s Death (Jedi)
My faves are (in no particular order):
Main Theme
Duel of the Fates
Qui-Gon’ Noble End
Across the Stars
Love Pledge and the Arena
Battle of the Heroes
Anakin vs. Obi-Wan
Enter Lord Vader
The Hologram/Binary Sunset
Princess Leia’s Theme
The Imperial March
Yoda & The Force
Luke & Leia
Confrontation With Count Dooku & Finale
Anakin’s Betrayal
A New Hope/End Credits
Den of the Rancor (Jedi)
I’d really love to know what John Williams thought of the prequels. Great music is the only sure bet as far as Star Wars films are concerned. Mainly because its not controlled by George Lucas.
IMO, Hayden and Natalie are ever so unworthy of having their own John Williams’ themes.
You might be interested in checking out the Music in Star Wars thread, a lot of people mentioned pieces they particularly enjoyed there.
Main Theme
Binary Sunset
Cantina Band
Princess Leia’s Theme
Battle of Yavin
(EPISODE IV)
Battle Of Hoth
Asteroid Field
Imperial March
Yoda’s Theme
Carbon Freeze
Clash Of Lightsabers
Rebel Fleet
(EPISODE V)
Pit of Carkoon
Luke and Leia
(EPISODE VI)
Dual of the Fates
(EPISODE I)
The Battle of Heroes
Anakin’s Betrayal/Order 66
The Immolation Scene
Padme’s Funeral
(EPISODE III)
The score from Episode II is not my favorite.
The Imperial March and Binary Sunset are my favorite.
Whachu’ talkin’ 'bout Willis!?!?
I always want to do that.
Welcome aboard darth willis!! You chose two staples of the Star Wars musical ensemble.
Superman: main theme
and
Superman: Love Theme
I really love Duel of the Fates and listened to it a lot after the Phantom Menace first came out. But I think my favorite John Williams theme of all time is the “Force Theme” from the first trilogy, even when Family Guy parodies it. 
Edit: Fixed the youtube video
Duel of the Fates is one of my favorites too, especially after seeing him conduct it live with the Boston Symphony and a full chorus at Tanglewood one year. Wicked powerful!
I really love “Duel of Fates” and i also really love “Welcome to Jurassic Park”
I have the three 2 disk remasterd additions from 1996. They title the tracks differently in this release than the original Soundtracks. but I’ll give it my best.
“Imperial March” is my favorite
“the Map room” from Raiders
“the Rebel Fleet/end titles” from Empire makes me want to cry everytime I hear it. It’s the first ( and one of only three times) I cried in a movie. When that movie ends and Han is gone and nothing has been won except escape… I was a mess for a few years!.
“Parade of the Slave Children” from Temple of doom. It’s basicly the theme for TOD. It’s every bit as good ( and maybe better from a music majors point of view) than the imperial march.
next is “The Emperor arives” it starts as a slow version of the Imperial march then goes quiet with a really bassy choral arangement. ( it’s the scene when Palpatine arives at the new death star. Another verion of it can be heard during the Luke Vader fight)
then who can forget the 1941 theme . That movie is why I went army! ( and I thought that i might learn to become Snake Eyes!)