This is a tough one for me. Both great stories.
I remember reading Slavers in some kind of collected best-of format and being totally blown away by it - the giant heads, the horror of the force feeding, the treatment of the slaves, totally useless Titus Smitus.. little dark comedic touches like potting peasants and the joke name of the story itself.
I also love Johnny and Wulf at the start on Smiley's World, Wulf catching fish in his aloha shirt.
The Killing though is packed full of jokes, action, crazy character names and designs and a bit of 2k social commentary - it's definitely one of the stories I'd give someone to read if they were starting off on SD. It's a belter, and it gets my vote this round.