Hmm tough one; so many fun times to choose from!
I'm going to have go with the whole story around Tinkerbots. At first she seemed like a fun, crazy disposable LTC who I could go on random shopping trips with and just have the biggest laughs with; but behind all that was an actual plot to be discovered and investigated – if you had the wits to discover it anyway!
I still laugh at how she reacted to me after I was reformed (again!).
That said i am a sucker for bloodshed, "area wide termination" i think was the quote you picked up on last time