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.
And because they’re relying almost solely on pure storytelling to carry the episode, they’re often some of the best episodes in an entire series.
They sacrifice plot, and theoretically compensate with character.