The Secret of Cassandra was a nice set of character studies, spoiled by a silly plot. Why on earth should the captain, charged with a vital military mission, stop off to pick up passing strangers? And the switch of loyalties of the computer Cassandra was most unconvincing.
The Stone's Lament is the best of these four. Benny and her colleague Adrian are stuck in an isolated house with a mad host who is obsessed with her; once again we have an intelligent computer with ideas above its station, all comes nicely together.
The Extinction Event had Miles Richardson making the first of his many appearances as Irving Braxiatel, and a story of the aftermath of planetary destruction. It seemed a bit implausible that this would be played out in the context of an auction, and I didn't find the denouement totally convincing.
The Skymines of Karthos was OK. I liked the concept of Benny going to the rescue of her friend, trapped in a troubled marriage and peculiar planet. The interaction with the dubious errant husband was also very well done. But I was puzzled by Benny's pregnancy - presumably a part of the background story I had missed?
So, if you are getting any of these, make it The Stone's Lament.