Signal encryption is unbroken. In fact plenty of other messengers (afaik WhatsApp too) use the signal encryption methods.

Signal doesn't save any data except your phone number and the last time you logged in (as Unix timestamp, so even without timezone).

For normal day to day ops and to move your friends away from WhatsApp, signal is the best alternative imo.

Simplex is even better in terms of privacy but the usability for non techies is hard(er)