Snapchat does not use end-to-end encryption for messages, so it doesn’t even belong in the conversation.

WhatsApp and FB Messenger are somewhat defensible choices since they at least use E2EE by default (Messenger did not until recently). However, there are a few good reasons to favor Signal:

1. It is open source. Interested parties can actually verify that Signal’s encryption claims are true. Interested parties can also audit new versions as they released.
2. Facebook/Meta, as a company, has a long history of tracking users, leaking user data, and even conducting psychological experiments on users without consent and in secret.
3. WhatsApp and Messenger only allow 6-digit PINs to secure your messages. With that PIN, you can decrypt those messages. Signal allows for longer alphanumeric passcodes.
4. Facebook makes no promises not to track your usage of Messenger or WhatsApp, only that the messages themselves are encrypted.

Additionally, you can set Android to use an ad-blocking DNS server without apps. In Settings > Network & Internet > DNS, select “Private DNS” and set the hostname to a custom server, like base.dns.mullvad.net (Mullvad’s DNS server is free to the public, does not require a VPN subscription).

The per-app controls sound neat! I might give that a try. Google killed the ability to restrict apps’ network access years ago, specifically so ads would always work. I’ve never tried a local VPN as a workaround.