whats better? Prison Architect or Rimworld?
That depends much on what you're looking for in a game. I'll preface this by saying that I've put maybe five hours into Prison Architect and about ten, or so, into Rimworld.
Prison Architect is, at the end of the day, a prison simulator. Rimworld, on the other hand, is a colony builder that was built on an engine originally developed for tactical combat games.
They're both great games, mind you, but they're different. Rimworld has more in common with Dwarf Fortress, I think. It's more about building and defending a fort/base/whatever in an environment that is mostly hostile towards you. Prison Architect is generally more of the "as hard as you make it" variety of game, from what I've found (unless you flip on the toggle that makes prisoners arrive daily regardless about whether you're ready for them or not).
If you're looking for a good combat game, go with Rimworld. If you're looking for a more personnel-related (read: micro-management) experience, I'd recommend Prison Architect.
Rimworld, I would actually recommend holding off on for a bit if you're leery of using mods and whatnot. As it stands I think it's a great game, but I don't know that it's worth the thirty dollar asking price with regards to the amount of content in the game right now. The game supports modding to a pretty impressive extent and there are already mods that add a LOT of content to the game if you're comfortable using them.
All down to brass tacks, it comes down to what kind of game you're looking for. As I said, if you want a better combat/survival game, go with Rimworld. If you want a better sim, go with Prison Architect.