"Radar's Report" contains perhaps the single best performance by Wayne Rogers on the series as Trapper contemplates killing a wounded POW.
Larry Gelbart said that was one of his favorite Trapper moments, citing that Trapper, as a character, could be really serious and gutsy at time.
I agree with Ranger, "Kim" is perhaps Trapper's defining, shining episode of his stint on the series: the titular Kim really brought out a paternal side of Trapper that was rarely seen except for those few occasions where he'd receive a care package from his girls back home; Trap also displayed some real emotion in that episode too - you feel the love he has for Kim and how heavy his heart feels at the thought of Henry sending him to an orphanage, you feel his angst and terror wandering aimlessly through the minefield, you feel his conflicting emotions when Kim is reunited with his mother.
"Check-up" also does a good job at showing what a proper farewell for Trapper would have been like when he really did go home between Seasons 3 and 4. That moment between him and Hawkeye in the Swamp after he finishes packing displays such genuine and sincere emotion, and the fact that Wayne and Alan were so close off camera made the acting in that scene so effortless, they probably weren't even really acting, they were probably playing it from the heart.
"Requiem for a Lightweight' is kind of a standard boxing episode that sitcoms seem to like to do back in the day, and while it doesn't really stand out as an episode of the series, it kind of gives you an idea of how early in the show's run, Hawkeye and Trapper were intended to be interchangable leads, and in this case, Trapper really carries the episode moreso than Hawkeye.
But really, one of my favorite things about Trapper was how whenever he and Hawkeye would be playing some kind of prank on Frank (hey, that rhymes), he could hardly ever keep a straight face: you'd see him stifling a smile, slowly start to smirk, or in the case of Pioneer Aviation, just bust out into laughter. Just goes to show you how much fun they were having when filming the show, I remember even Jamie Farr saying how much he loved to go to work everyday and go home with his sides hurting from laughing so much.