Android is a highly secure operating system with full verified boot, strong sandboxing, a permission control system, modern exploit mitigations, and more.
Google Pixel phones are the only secure phones as they fully support verified boot, use the custom Titan M2 chip, use the Trusty TEE OS, and can effectively randomize the device's MAC address. There is a reason why GrapheneOS only supports Google Pixel phones. Do not even think about buying a different phone. All other phones are a security nightmare and should be avoided at all costs!
Reading Material: https://source.android.com/security/features https://source.android.com/security/verifiedboot/ https://security.googleblog.com/2021/10/pixel-6-setting-new-standard-for-mobile.html https://source.android.com/docs/security/features/trusty#whyTrusty https://android-developers.googleblog.com/2017/04/changes-to-device-identifiers-in.html https://madaidans-insecurities.github.io/android.html
Most custom operating systems substantially weaken the Android security model. Never leave your bootloader unlocked and do not root your device. If your phone does not support GrapheneOS, use the stock operating system.
Reading Material: https://privsec.dev/os/choosing-your-android-based-operating-system/ https://www.privacyguides.org/android/ https://madaidans-insecurities.github.io/android.html#custom-roms
GrapheneOS is a privacy and security focused mobile OS with Android app compatibility developed as a non-profit open source project. It's focused on the research and development of privacy and security technology including substantial improvements to sandboxing, exploit...
Open-source mobile operating system, seamlessly integrating with Google services, enabling extensive app support and hardware compatibility across brands.
You should never use F-Droid as it substantially weakens the Android security model. Most people should only install apps from the Google Play Store. If your threat model requires not logging into Google, you can use the Aurora Store but must understand the risks of using third-party app stores. Source: https://wonderfall.dev/fdroid-issues/
Official Android marketplace for apps, games, books, movies, and more accessible via Android devices and web browsers with user reviews for each item.
Use Chromium browsers only. Firefox on Android still does not support site isolation. You should access most websites including YouTube, Twitter, and Reddit inside the browser instead of their apps since websites in a browser are much less privileged than an app.
GrapheneOS users should just use Vanadium. For stock Android users, use one of the browsers listed below. Mulch was considered as it is a hardened fork of Chromium with timely updates, but is not listed here as it is not available on the Google Play Store but F-Droid.
Reading Material: https://grapheneos.org/usage#web-browsing
Web browser built on an open-source platform featuring multiple account support, integrated password manager, dark mode, real-time translation, and seamless cross-device syncing.
If possible, convince your family and friends to use Signal as it uses end-to-end encryption by default, can hide metadata, has a good track record, and is recommended by many security researchers. Otherwise, use Google Messages.
An encrypted messaging app focused on privacy, supporting texts, calls, photos, videos, files, and group chats, with no ads or trackers.
Messages is Google's communications app for 
Android to helps send and receive SMS and MMS messages. You can also send group texts as well as your favorite pictures, videos and even audio messages to your contacts.
Swiss-based VPN that ensures online privacy with a high-speed network, advanced encryption, and no-logs policy, offering a free version. Supports multiple platforms and unblocks content worldwide.
Shelter is a Free and Open-Source (FOSS) app that leverages the “Work Profile” feature of Android to provide an isolated space that you can install or clone apps into.
Auditor is an app which leverages hardware security features to provide device integrity monitoring for supported devices. Currently, it only works with GrapheneOS and the device's stock operating system.
Use stock apps when possible as installing third-party apps gives you another party to trust and increases attack surface. Unless the app is something you need (such as WhatsApp), only install third-party apps either if there is no stock app replacement or if the stock app can be uninstalled from the system. Choose apps that require as few permissions as possible.
Feeder is a fully free/libre feed reader. It supports all common feed formats, including JSONFeed. It doesn't track you. It doesn't require any setup. It doesn't even need you to create an account!
A minimalistic notes app. Notally it's extremely light, minimalistic and elegant. There are minimal dependencies and lines of code. (All without compromising on readability).
Privacy-focused GPS app with offline maps and community development, featuring real-time navigation, no location tracking, and open-source software.
This is a modern camera app focused on privacy and security. It includes modes for capturing images, videos and QR / barcode scanning along with additional modes based on CameraX vendor extensions (Portrait, HDR, Night Sight, Face Retouch and Auto) on devices where they're...
Simple Android PDF viewer based on pdf.js and content providers. The app doesn't require any permissions.
Reading Material: https://source.android.com/security https://privsec.dev/os/android-tips/ https://www.privacyguides.org/android/overview/ https://madaidans-insecurities.github.io/android.html https://github.com/beerisgood/Smartphone_Security
Comments
Replace Chrome with brave or bromite (or Vanadium on GrapheneOS) and the PlayStore with AuroraStore for better UX and privacy
Aurora Store lacks important security features including certificate pinning, still requires the legacy store permission, among other security issues.
Bromite is much slower to update than other browsers.
Sources: https://gitlab.com/AuroraOSS/AuroraStore/-/blob/26f5d4fd558263a89baee4c3cbe1d220913da104/app/src/main/AndroidManifest.xml#L28-32 https://gitlab.com/AuroraOSS/AuroraStore/-/issues/697 https://privsec.dev/os/android-tips/#aurora-store https://divestos.org/misc/ch-dates.txt