I don't know if I really have a "saddest", but I definitely had some "best" ones.
LSU-Baton Rouge: best dinner by far with tons of residents, faculty, PD, and it was at the PC's house where she cooked the most incredible meal. The house was gorgeous and was down the road toward LSU main. Those people know how to throw a party!
Runner up- U Pitt. "The Church" is a fabulous restaurant/pub with some of the best pizza and beer, and the UPitt guys are close behind the LSU guys in terms of knowing how to drown sorrows!
Runner up- Case/Metrohealth- another group who knows how to hang out and have a good time. Great beer, great pizza, and the people were what made it. No one sitting around complaining, and everyone got along very well. Lots of residents.
Iowa, OSU, Mayo, Peoria, and Scott and White also had great dinners that get them a very strong honorable mention, and anyone who has met FoughtFyre at a Mayo dinner can attest to how easily he breaks the ice for a four star grade on atmosphere!!
Tipping the scale toward average dinners we have Penn State (only 2 residents and my wife and kids..but toward the end of the season), Duke mostly because a lack of social skills on the part of some of the residents that night (but their lunch the next day had different residents...much more social).
Christ, Texas Tech, and Geisinger had no official get-togethers the day before but it had no affect on how much I liked them at all. Had I not had adequate exposure to their residents then I might have cared.