That depends on who you talk to. Signal and Telegram use the same exact security protocol. Most hackers use Telegram but peope in Congress use Signal.
Open Whisper Systems was started by the son of a ultra wealthy Russian oligarch. The end to end encryption standard is becoming a normal thing now but the server in the middle is always going to be a problem. Based on what I read on secure messaging — encryption alone is not going to fix the problem.

https://news.ycombinator.com/item?id=12880520

https://fossbytes.com/best-secure-encrypted-messaging-apps/