> In an ideal world, I'd host it myself for everyone I communicate with to use, but without federation that's not a possibility, so given a choice between Signal and WhatsApp, the decision is hands-down Signal.

If that's the only choice, maybe yes. Though the installed base of whatsapp is so big I could not leave it right now anyway. So Signal would only be extra.

But for me to voluntarily promote an app it has to be a lot more open than Signal. Even if other people around me start using it I'll probably be the last to move.