Is Ren'Py pretty much the best visual novel engine, or are there others that are just as competitive?

If my question is too broad, I'll try to narrow it a bit and ask... If one were to do a large Visual Novel project, and wanted to use a Visual Novel catered engine, is Ren'Py the best in features and in performance?

It depends on your knowledge and if you need any special features.

What I have seen, people who make VN use Renpy or use a generic game engine, such as godot or unreal, even game maker.

Renpy is much easier to use if you want to create a VN (If you don't know anything about programming, watch one tutorial in an afternoon and you are already creating your VN), it has a very large community that can help you in case of doubts and allows you export to different systems and that is why it is so popular, but it is limited to 2D VN or at best a pseudo 3D.

I haven't seen Renpy have any problems with games with several gigabytes of content and hundreds of thousands of words of content. But if you want to do something more complex, like minigames, you have to learn python and pygame and it's not very resource efficient.

Engines like Godot or Unreal can be more efficient and have many more features, especially if you want to create a VN with 3D content, but since they are not specialized VN engines, you cannot go there and create a VN without knowledge and prior effort in programming and master the tool.