I'm opportunistically supporting more secure messengers by "digital osmosis".
Next to WhatsApp I also have installed:
1. Signal
2. Threema
3. Telegram
And I will use those (in described order) if possible.
Threema seems to be comparatively popular in Germany, while Telegram is at least not among my peers and Signal (the one recommended by Schneier and Snowden) is only used by my gf (b/c I installed it for her).