As far as competitors go, the list is not very long. Sugarcube/Twine works ok, but tends to bog down as the projects grow large because it doesn't have a good way of breaking up the core logic across different files. The save system is also a bit of a problem since the in-browser saves tend to get lost in version updates. QSP is just a buggy confusing mess every time. People try to shoehorn RPGMaker into doing the job but it is just so clunky and slow. Custom engines, typically built in Unity, are almost always massive resource hogs and lacking in one or more of the basic features Ren'Py provides by default. Plus there is just the community aspect of it, with Ren'Py having so many developers there is a lot of institutional knowledge to be had. If you run into a problem you are probably not the first, someone else has probably solved it already.