I generally like commentaries most, but Bahimiron is right that most suck. Some good ones:
This is Spinal Tap: Michael McKean, Christopher Guest and Harry Shearer do a mock-review in character as though it were a real documentary, with the angle that Marty DiBergi really screwed them in his portrayal.
Almost Famous: Cameron Crowe is there with a troupe of crewmembers, and his real life mother. Who is hilarious, and says stuff like “You had Frances McDormand in bare feet there. I never go barefoot around the house, I think it’s disgusting”. Also, cue uncomfortable laughs from Crowe during the scene were the kid loses his virginity. It’s also cool to hear a ton of rock history from Crowe, and some of his real-life adventures that the movie was based on.
My Basic Instinct DVD has a commentary by Camille Paglia for a “feminist” analysis of the movie (spoiler: she liked it). You can tell she’s reading off notes, but it was still quite interesting.