Module builders SystemJS vs Webpack

No. Webpack SystemJs
1 Well matured  Based on draft module loader specifications, so it is subjected to change till it is finalized.
2 Importing new libraries/modules are fairly simple and easy with just import statements or require statements.  Need to mention the exact/correct path to external libraries or packages in systemjsconfig.js. Whenever the project folder structure changes, you need to update config with new location structure.
3 Webpack can handle any resources by adding proper loaders. e.g., css-loader, typscript-loader, style-loader, sass-loader etc.,

System JS doesn't come with default builder, so you have to either depend upon task runners like grunt or gulp tasks to perform the tasks.

Update:

SystemJs builder exists but it is still in its early stage and requires time to mature.

4 Official site is well maintained with links to all major loaders provided in the official site to avoid confusions

Not much, you need to resort on StackOverflow for answers.

5 Webpack provides out of box feature which does ES6 modules - tree shaking

Need to rely on rollup or such plugins to perform Tree Shaking 

6

For Angular development, you will find required amount of resources to kick start without pain. One such wonderful starter project link is provided below

https://github.com/AngularClass/angular-starter

All official Angular examples are provided using SystemJs module builder. So it would be easier getting started with SystemJs + Angular.

Note: Angular CLI tool now works using webpack. And current development sample code are based on Angular CLI.

A very good starter project using SystemJs and gulp based build system.

https://github.com/mgechev/angular-seed

7 It has a built-in web development server, that can keep all generated dev. resources like css, js etc., in-memory and provides a faster development experience.

Requires a build & run systems like grunt or gulp coupled with http-server for development.

Currently, Angular CLI provides live server & reload features which can complement for development.

8

Very well supported by open source community. It has a very good number of sponsors and backers.

SystemJS is based on module system specifications drafted by W3C, so it needs some time to gain momentum to reach a matured level.

9

Can use regular expressions while requiring an external module or resources. See example Context Replacement plugin for optimizing Moment.js

Not supported