Hmmm,
I'm thinking Swinetrek. From about day 1, it's been the playset I've been looking forward to the most. I guess it all comes down to personal taste. I like Chef and all but Pigs in Space has always been one of my favorite sketches. So that's the one playset I REALLY want. it also has use for the most figures (not counting Robo-Rabbit in ML) And I'm not counting the EM set since Animal is the only one who actually 'fits' in there.
--Matt