Of course its no new thing that BBM is now the most popular app on Android. To download any of them simply search for them on Playstore.

As for the best among them, in Mymobnet! it is said that
Full post link: http://www.mymobnet.com/blackberry-messenger-whatsapp-best/

Now Let’s look at the advantage WhatsAPP has over BBM
• it is supported across wider platforms including Java based devices and Symbian
• It is more popular and a better alternative to phone SMS
• More and better emoticons

Let’s also look at the advantage BBM has over WhatsApp
• It has a better User Interface
• It supports extra features like live friend’s updates and it can show what song friends are listening to
• Supports group chat

Link to full post here http://www.mymobnet.com/blackberry-messenger-whatsapp-best/