What is the best practice for importing angularjs using webpack?

You can just require angular in all modules (files) where you need it. I have a github repository with example how to do that (also using webpack for build). In the example ES6 import syntax is used but it shouldnt matter, you can use standard require() instead.

Example:

import 'bootstrap/dist/css/bootstrap.min.css';
import './app.css';

import bootstrap from 'bootstrap';

import angular from 'angular';
import uirouter from 'angular-ui-router';

import { routing} from './app.config';

import common from './common/common.module';

import featureA from './feature-a/feature-a.module';
import featureB from './feature-b/feature-b.module';

const app = angular
    .module('app', [uirouter, common, featureA, featureB])
    .config(routing);