If you mostly use iOS and macOS devices, you may prefer using services that come from Apple. Although Google Photos is a well-integrated app, rarely is there an option better than a built-in service that's designed specifically for the device you're using. You may miss the fact that iCloud has a slightly better user interface on desktop computers. Also, it's much easier to free up storage space using iCloud. When you delete a photo, it's completely removed from your device since iCloud only offers to sync your images.