Easy. iPhone X.
When looking at the security of iOS devices versus Android devices, we immediately eliminated all Android devices from the equation. On Android, messages and photos are not permanently deleted. When files are "deleted" on Android, really all that happens is the operating system labels the disk space that stores the file as free space. The data is still there, and off-the-shelf data recovery tools can easily recover it. There are numerous free apps in the Google Play Store, such as Secure Eraser, that will allow you to delete these files properly, however, it is inconvenient an impractical to run this frequently. Tools like this write over the so-called free space with random data.
Then it comes down to the iOS device with the best camera. As one might expect, the newest device usually has the best camera. In practice, the camera on all iOS devices is more than sufficient for just about all users.
If forced to use an Android device, the Google Pixel is the clear winner.