My answer is always the same:

Depending on your threat profile and how you use the app.

Telegram makes communications more secure while maintaining a feature set that is conducive to reliable and enjoyable. They have a strong privacy policy, the app (although not the server, which is indeed sad) is open source under GPLv3, and they have submitted themselves to multiple independent audits. They use phone numbers for signup in order to reduce spam (there are multiple ways around giving them your number) and for those who want a simple transition for family and friends to discover one another on Telegram. You can choose who to share that number with.

SimpleX is a decentralized messaging protocol that has also been subjected to audit. (https://github.com/simplex-chat/simplex-chat/blob/stable/blog/20221108-simplex-chat-v4.2-security-audit-new-website.md) It addresses novel issues not with the privacy of message contents per-se, but with meta-data leakage. They require no number to sign up, and the addressing system makes it quite resilient to spam.

Your IP address is still exposed to the relays you connect to. Whether they log those IP addresses breaks down to a case of "trust me bro" the same way it does with any web service. On my Nostr relay, I do not retain any IP data, but how would *you* the savvy user verify that?

Using multiple redirections, there is possible additional security from very advanced forms of traffic profiling, such as timing attacks.

The tradeoffs are a more complex messenger, very unreliable notifications, difficulty in establishing connections with new contacts, and a more limited feature set.

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My honest opinion:

The best messenger for privacy is the one your contacts will use, and has the feature set you require. Getting my friends and family to sign up for Telegram was very low friction, and now 90% or better of my comms have a decent level of security vs. none before.

If I am concerned with privacy from a state actor, I would not use Telegram. I would also not use Nostr without a privacy preserving client that disabled all media fetching, etc. I *might* use SimpleX.

For 99.99% of users, using *any* e2e messenger + a VPN is extremely private compared to any other option.

Obligatory Disclaimer:

These are my opinions, and I have no intention of shitting on any messenger. Individuals should use what fits their threat profile and they can get their contacts to cooperate in using. Sensitive information should not be shared on the Internet, period.