I’ve so far only listened to the DVD commentaries for each. ANH and ESB are the best. Lucas keeps his “I had everything planned” to a minimum and actually gives some great insight into the process of developing the story and structure of the films. Kersh is a very welcome addition to ESB. He sort of narrates a lot of the film but usually as a way to point out moments that build character.
ROTJ might be the worst of all six. For long stretches no one talks and when people do they just seem bored.
The PT ones are actually pretty great, and give some nice insight into the creation of the films (my favorite bit, from the ROTS commentary I think, Rick McCallum says something about how he still didn’t have a script weeks or so before filming started). Fascinating stuff from all involved. We give the films shit for all the CGI, but from technical perspective, all that stuff is pretty impressive. The FX guys point out FX shots and manipulations that I would have never noticed.