It will be depending on the person you are on boarding...

A normie non tech savvy and little to none understanding of the power of decentralization and relay management.

Primal or Damus for mobile or desktop.

A tech savvy individual understanding the above and whom consider his CyberSec as a serious matter:

Android: Amethyst @nprofile1q... , 0xchat
iOS: 0xChat @nprofile1q...
Desktop: nostrudel.ninja