One of those versions is offered via the Google Play store and the other is offered directly via the WhatsApp website.
If you want the most up to date app, you want to be using the version offered via the website. This version was recently updated with a new feature that allows the user to see how much data they have used with voice calling. The information shows data used for outgoing and incoming calls from other users of WhatsApp.
This bit of information is important because there is no official voice calling feature available at this time. By adding in the ability to see how much data is used by making and receiving calls, WhatsApp clearly plans to launch voice calling soon. The images here are supposed to be what voice calling will look like on the app.
Anyone wondering why WhatsApp started to ask to turn Bluetooth on, the voice calling feature is why. It appears calls will be started just as you normally would start a chat with someone, by simply pressing their name. Call recording is also tipped to be possible. It's unclear when the voice calling feature will launch officially.
