Check:

https://securemessagingapps.com

and rate the security 
green=3  yellow=1  red=0

Results:
 
1. Threema = 85 = WINNER
2. Session = 79
3. Signal = 77
4. Wickr (Amazon) = 62
5. Element / Matrix = 59
6. WhatsApp = 34
7. Telegram = 29
8. Apple iMessage = 25
9. Facebook Messenger = 25