Coincidentally, I just downloaded Twine and tried to understand how it works. I love it; it's just what I've been looking for. It's perfect for narrative, not as schematized as Inkle. I don't know Renpie, but I think I'll give it an eye in the future.
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Ren'Py is more for visual novels. If you're just doing regular text-based stories, I'd recommend sticking with Twine. You can do normal text-only stories in Ren'py, especially with NVL-Mode, but Twine is lighter and can be simpler to learn for people starting out with the programming side of things.