I'm going to parrot what people in the GrapheneOS community would say: "The most secure place to get apps from is Accrescent. If an app isn't available there, the next best place is the Play Store itself with an anonymous Google account." Some bother to add that Obtainium+AppVerifier can be used if it isn't available for either of those methods. Anyways, they're very stingy about where they get their apps from.

Here is my take: Despite claims of F-Droid and Aurora Store having security issues, I don't care. It's based on your threat model and personal preference. Google may soon be forced to open up Play Store apps to more third parties, so more secure methods of getting them may crop up in the future. You'll really never have a 100% private way to get apps, that's the unfortunate reality of how things are. If your threat model is against Google and supply chain attacks, those limit your options down to some less-than-convenient methods. If you do decide to use AppVerifier, do note that you only need to verify the hash once and you're good for the rest of your phone's life.