Personally for me, “Mail Call Three” (6×21) is my favorite, but there’s a silly story behind that – late one night before I really started watching the show, I was channel surfing, and while checking out Hallmark Channel, there was the scene where B.J.’s trying to get Radar to put through a call in the middle of the night, and in his frustration, starts shaking Radar’s teddy bear, which upsets him; so when I saw this episode in its entirety for the first time, I was hooked, lol. “Mail Call Again” (4×15) is my second favorite, mainly because of Frank’s call to his wife, while Margaret avesdrop from Radar’s phone, lol.