The mere fact it hoovers up less metadata alone makes it more private. I also trust the developers more way way more than I trust Facebook. That's a personal preference though and if you trust WhatsApp and don't mind that it leaks contacts and other metadata to Facebook to profile you then use WhatsApp.

If I wanted to I could install a fork of Signal that doesn't require Google Play [1] and run it on any non-Google Android build. I would do if it wasn't for the fact I'm currently using an iPhone.

[1] https://langis.cloudfrancois.fr/