To find out who your best friends on WhatsApp are in Whatsapp

To find out who your best friends on WhatsApp are, if you have an iOS device, head to Settings 

-> Account -> Storage Usage. Here you'll see a list of the people and groups you message on 

WhatsApp along with the total number of interactions you've had with that person/group. 

If you select "Size" at the bottom right of the screen you can see who you have spent the most 

data WhatsApp-ing.