I have used riotjs for about two years now and it was always my first choice for building reactive components. Although I have experience with both angular and react, I get tired of them quickly. What's so beautiful about riot is how easy it is to understand yet powerful to do anything I need. There is only minimal Knowledge required to get started and almost everything you learn the way, can be applied somewhere else outside riot too.
Yes - it takes a lot of time and effort to master these tools. But once you get there, you don't want to miss it. And I don't mind investing a couple of hours to get instant previews of my changes to the codebase and automated minification, polyfilling, etc.