There are many ways to make your communication faster and safer but in my opinion you should use WhatsApp or its modded version for this purpose. For a secure communication system, using WhatsApp is better than using other methods. If you use WhatsApp, you can also know if the recipient has received and read your messages. But using the modded WhatsApp version Like
Fm whatsapp 2023 ,it will enable you to hide your last scene and other similar features, now it's your choice which one you want to use.