There are tons of threads about the best app install method discussions on the forums you can refer to, including this recent one.
For normal apps, using the Play Store with an anonymous account offers the best balance between privacy, security, and convenience. For FOSS apps*, I use F-droid to browse available FOSS apps, then use Obtanium to download them directly from source, which alleviates the security issues of F-droid (more on that below). If the app isn't downloadable via Obtainum for whatever reason, then I use F-Droid Basic with a custom repo if possible, then if all else fails, only then F-Droid Basic to download it from the main F-Droid repo.
However, I am not new to open source software, and I was always under the impression that f-droid was superb. Not exactly sure why now it's not necessarily a safe source now and that a sandboxed Google play is better?
F-droid is amazing for privacy, but it does have some security issues. This is a great write-up on the security issues of F-Droid, and PrivacyGuides also has an informative section on the security issues of F-Droid:
Due to their process of building apps, apps in the official F-Droid repository often fall behind on updates. F-Droid maintainers also reuse package IDs while signing apps with their own keys, which is not ideal as it gives the F-Droid team ultimate trust. Additionally, the requirements for an app to be included in the official F-Droid repo are less strict than other app stores like Google Play, meaning that F-Droid tends to host a lot more apps which are older, unmaintained, or otherwise no longer meet modern security standards.
As indicated in the other post, the *FOSS app refers to:
- Apps that are only available on public repos/F-droid and not on Play Store
- For users who want to avoid as much Google code as possible
- ex: Google Firebase Messaging that is included in Bitwarden's Play store version but not in the F-Droid version
- Apps that offer better experience on the F-droid version
- ex: Apps that require in-app purchase on the Play Store version, but offer the full functionality on the F-droid version, such as Tasks.org