Blatantly the best episode is You Only Move Twice. For me, this moment is the absolute peak of the series, never to be matched again:
Homer walks into a giant missile hangar to talk to Scorpio.
Homer: You got any sugar around here, Hank?
Scorpio: Sure, here you go, Homer. (Scorpio dumps handfuls of sugar into Homer's cup straight from his jacket pockets) Sorry it isn't in packets. Want some cream?
Homer: Yeeeeeeeeeee... no.