Ask HN: Angular2 UI Frameworks ng-bootstrap, ng2-bootstrap or material2

With today's release of angular 2 stable we're looking to migrate a prototype app built with RC4 + ng2-bootstrap to angular 2 stable.

This presents the chance to re-evaluate some our UI framework choice. For both of the hot contestants material and bootstrap there are multiple libraries available. Obviously they're all beta/alpha, bootstrap 4 is alpha and in flux as well. We're primarily targeting the desktop and want flexbox.

#1: What do you consider the pros and cons of bootstrap 4 vs material?

#2: What is your opinion on these bootstrap4 libraries: Built by angular ui team: https://github.com/ng-bootstrap/ng-bootstrap Built by valor software: https://github.com/valor-software/ng2-bootstrap

This discussion of "different goals" between the two bootstrap libraries left me clueless unfortunately: https://github.com/ng-bootstrap/ng-bootstrap/issues/164