Personally I gotta pick the season 5 episode 'Souvenirs' by Burt Prelutsky and Reinhold Weege. It's a more subtle slice-of-life style story contrasting the shows usual dramatic style. What it lacks in spectacle it makes up for in narrative cohesion; every character and plot element get equal time in the spotlight.
Potter using Kliger's section 8 attempt to his advantage was a clever twist
B.J. and Hawkeye in post-op with the kid is sweet yet heartbreaking
Margaret punching Stratton and giving Frank what for *chef's kiss*
All around underrated ep.