At my time of adoption, Telegram had a better feature set and I wasn’t honestly super focused on the privacy minutia. Knowing what I know now…I guess Signal, but honestly I’d probably go even more niche if I was after something truly private. Like P2P messengers or something like that. I don’t really treat any messaging platform as fully private. If I really need something guaranteed to be private and I don’t want to try to convince a friend to install a new, even more obscure app, I’d probably just encrypt text files and generate keys for each other and send them via something, maybe email idk.