I’ll go first.
Winner:
Breaking Bad, season 3 episode 10, “Fly”
Honorable mention:
Community, season 3 episode 10, “Cooperative Calligraphy”
PS: I’m having a hard time categorizing these as real bottle episodes since they don’t feel cheap or “fillery” at all, but they are at least spatially and plot wise confined.
what is a “bottle episode”?
When a show ran out of money or wanted to spend extra on other episodes they’d either do a clip show or a bottle episode. A bottle episode traditionally uses only standing sets and existing cast under contract, with no special props or costumes.
Usually called a “bottleneck episodes” because the characters are trapped in a room together. So much of the episode is dialogue based.