I never enjoyed the swamps level. Too many tricky jumps and I just didn't like the feel of it, for some reason.
Escape from Theed and the game's final two levels are great for action.
Otah Gunga is cool because you can kill lots of gungans and it doesn't matter!
Coruscant is also good, as long as you play as a jedi.
Mos Espa and the podrace - now you're talking! Best two levels of the game - real sense of freedom and the chance to go completely crazy!