On the whole, rST for sure has the right stuff. Having a document model and a nice standard extensible mechanism for syntax really helps. It's been my favorite.

But even when writing my last paper I used Markdown (+pandoc) because I had a coauthor and Github et al. have made it more familiar to so many more people. Maybe in niches like the Python community but it's a distinctly minority option, at least where I've worked.