- Full form
APK: Android application package or Android package kit.
AAB: Android application bundle.

- Submission
APK: is submitted and later downloaded in the same form as it is created.
AAB: is split into smaller APK files. Each split APK corresponds to a specific device configuration.

- Installation
APK: can be used to directly install an app on an Android device.
AAB: cannot themselves trigger installation. They defer APK generation to Google Play.

- Size
APK: ensure larger app size because all resources are downloaded to the device irrespective of their need.
AAB: ensure smaller app size because each split APK contains device-specific resources.

- Dynamic features
APK: all feature-based resources are stored within the APK file.
AAB: dynamic feature resources are stored on Google Play and called upon when needed.

- Asset packs
APK: all assets are stored in the main APK file.
AAB: all assets not needed to install the app are stored on Google Play.

- App churn
APK: larger app size causes greater app churn.
AAB: smaller app size causes lower app churn.

- Storage efficiency
APK: unnecessary resources take up a lot of device storage and reduce efficiency.
AAB: is more efficient in terms of space.