Given that the post-apocalyptic train has been passing by us for some time now as we wait at the crossing, the element I would be looking for is the reason for the telling of the story. Even the most burnt trope can be made enjoyable if it has a backbone, a purpose that goes deeper than the props of the trope. There's surface story and there's deep story. There's skin and there's meat. What's the meat? You don't have to answer that - it's rhetorical - but that's the element I would be looking for in such a story.
I would think it'd be both. I wasn't planning on having only slaves, that wouldn't work. I was thinking more of a Spartan or Roman style rule, with both free citizens and slaves.
Take a look at Europe after the collapse of Rome, 500-1000AD. A strong central government collapsed, taking down continent-wide trade, security, maintenance of roads, canals, ports and aqueducts. Without aqueducts cities which easily supported 100K and upward populations could not support more than tens of thousands. Back to subsistence agriculture. Dominated by multiple petty warlords with wide variation in quality of government, no unified currency, barter re-emerges. Loss of literacy and education, constant warfare.
And let's not forget post-Black Death times. I'm not into history that much, but from what I know the Black Death would count as an apocalypse of sorts. As for what happened after, I'm not sure but I think I read something about because of the death toll the serfs were able to unite and demand better working conditions or something like that.
The Black Death ended serfdom because no one was around to ensure that they stayed to tied to the land, and the uninfected population was on the move as refugees to avoid areas where it had broken out. When they got to a new location, no one cared if they were serfs on the run, and manpower was so short they could work for a wage... this was the beginning of wage labor.
I'd like to see a lot of the soft apocalypse kind of thing. Like, grass and flowers in walmart, or houses with moss and flowers inside. It's interesting to see what nature takes back when not held back by humanity.