ApkPure vs Aptoide vs Uptodown

If security is the main concern, I would not put any of those three in the same bucket as the developer’s own download page, F-Droid, or Play/Aurora. With APK mirrors you are trusting their update pipeline as much as the app developer. I’d first see whether Obtainium can follow the app’s official releases directly; if not, use a mirror only per-app, check the package name/signing certificate, and avoid making it your general store. Between those three, Uptodown is usually clearer about versions, but I’d still treat it as a fallback rather than the safest option.