I have worked with both, and I would only use Twine if I were developing a text-based game. It's a nice engine to work with, but RenPy offers more functionality out of the box and is widely used. It takes some time to get used to the syntax for writing text, though. Writing something if quite a lot faster in Twine, and sometimes I use it for quick prototyping. Write some text with a few decisions, and try out if it makes sense. If I like the text and paths, I will put it in RenPy.
Both are valid options, though. Just use whatever you're most comfortable with.
Both are valid options, though. Just use whatever you're most comfortable with.