I'm using SystemJs + JSPM and it's awesome. I previously made use of bower + requirejs. I love how JSPM automatically populates the config.js file so I can start importing whatever I installed straight away. SystemJS loads pretty much any module format so it was easy to use AMD modules while I was migrating to CommonJS. I recently moved over to ES6 modules without having to touch my SystemJS/JSPM config. I've not really looked into Webpack. It seems to be more popular than SystemJS. When I was considering it, the docs were not that great.