It's always gonna be a moving target. Wife and I started using Telegram because it wasn't monitored like Facebook Messenger (which I don't have an account for) or WhatsApp. Now people are saying Telegram isn't good enough, use Signal. It's still good enough for us. I also have Signal. No one I know uses it, but I have it in case they wanna start using it.
Honestly though, iMessage is secure enough for most people. Basically texting through Apple servers.
But any security or privacy expert will tell you that you need to determine your own threat model. No one else can tell you what that is.