accounts-password-client-side | Use Meteor 's accounts-password package | GraphQL library

These approaches are essentially the same for the authentication itself. What you are pointing out is more about what mobile platform to choose to develop and run mobile projects.

In the first case, you use Meteor's built-in Cordova platform to run the app and Meteor's compiler and bundler plugins (like TypeScript package or Meteor core packages for Babel and UglifyJS etc) to develop the app. In the second case, you develop and run the app solely on Ionic 2 CLI.

But from the app logic point of view these approaches are absolutely same: you import the same Ionic 2 components and use the same Meteor packages with the only difference in the second case is that these packages are now NPMs not Atmosphere ones (essentially though they contain the same scripts since these NPMs are built from Atmosphere packages).

The reason why What’sApp clone is built in that way that differs from the Socially’s one is simply described in the README of the What’sApp repo (see https://github.com/Urigo/Ionic2CLI-Meteor-WhatsApp). If to repeat: since Ionic is a one of the best Web frameworks that specializes solely in building mobile apps, it’s reasonable to guess that it’ll be (and likely it is) much more powerful in building them than Meteor itself. From that point of view the second approach seems more future-proof, I would say. You could think even of building your project in some way that will allow you to substitute Meteor easily with some another framework if you decide to use it at some point in the future.

If you are though concerned about using those NPMs mentioned in the second case (e.g., if the process of building them doesn’t look transparent to you), you could try this project https://github.com/Urigo/meteor-client-bundler to bundle Atmosphere packages you need into separate scripts and use them after.