The best engines for what? It depends on the games I want to make. Is it the fault of Ren'Py that I never got much done with it? And if you're asking Twine, which story format? Because I like both SugarCube and Chapbook, for different purposes. But in the end I had the most success with my own custom EightWay Engine, even though I only made two complete games with it. And like above, that's only a renderer.