The official WhatsApp app on Windows phone just updated to version 2.12.318.0 and has brought with it some minor refinements to the previous update which introduced dynamic chat bubble resizing to match the amount of text in a chat, improved notifications that clear once the app is opened, more detailed Live Tiles, and a cleaned up app information screen.
Unfortunately the update does not bring over some of the newer features being tested in the WhatsApp Beta app such as the ability send larger video files and attach documents.
The WhatsApp Beta app also updated this week (now in version 2.12.314) and has added a new icon to the recently added document attach button as well as a variety of different language options for in-app messages. Video compression has also been improved for when sending clips to another user.
The WhatsApp Beta app is used to test certain features with a small group of users before rolling them out to the general public. Other companies such as Facebook also use beta versions of their apps for similar reasons.