I'm using RequireJS in my main project, in production. The latest modules have the es6 module syntax, so I'm transpiling them via requirejs-babel. I've iterated to replace RequireJS with Alameda and now Cajon, but those three are from the same author so those are just drop-in replacements. For the new projects and the develop branches, I'm using jspm and I'm loving it. However, you can't just use SystemJS as a drop-in replacement for RequireJS if you use loader plugins. About webpack... I guess I didn't learn it on time and it might get superseeded by jspm and rollup, so I guess I'll pass. Same goes for browserify.