[meatmanek]

For a slightly different perspective (1:1 chat instead of Slack replacement) I've had a better experience with Keybase than Signal or Telegram for end-to-end-encrypted 1:1 conversation.

Telegram's "Secret" (e2ee) chats are device-specific, which pretty much disqualifies it for regular use.

For Signal, I've consistently found that if I'm logged into three devices (e.g. two laptops and a phone), my phone will buzz and a notification will appear but then immediately disappear. If you don't notice the vibration, you'll miss the message until the next time you open the app.