Google Allo vs Google Hangouts

Google Allo
Google Allo is a smart messaging app that helps you say more and do more. Express yourself better with stickers, doodles, and HUGE emojis & text. Allo also brings you the Google Assistant.
Google Hangouts
Google Hangouts is a live video chat app. It allows to share your screen, collaboratively draw on a whiteboard, edit Google Docs documents, create broadcasts for the unlimited number of viewers. Splitted into group chat app and videoconferencing app. Secure Google Hangouts alternatives are Signal and Telegram.
Google Hangouts has better video than Google Allo

2017 - Google adds audio calling to Duo and file sharing to Allo to keep up with Google Hangouts

Google announced the changes to its video calling app Duo and messaging app Allo. When Duo originally launched, it had an odd omission: You could use it for a video call, but not an audio-only call. Now, Google fixed this; the company says audio calls will work well even on slow connections and won't eat up much data. Google Allo is also getting an important feature: file sharing. The option was a highly requested one in some markets, and now all Android users can use the app to share .pdf, .docs, .apk, .zip, and .mp3 documents.