ntfy for push notifications where possible

Signal/Molly (hardened Signal fork)

SimpleX

F-Droid Basic for apks only on f-droid. I highly recommend F-Droid Basic over F-Droid it allows for unattended updates.

As far as installing apps, a good rule of thumb is:

apk direct from dev installed via Obtanium > apk via F-Droid Basic (signed by the dev from their official repository is considered more secure than signed by f-droid) > Aurora > Google Play