WhatsApp doesn't just support¹ Signal's end-to-end encryption, it enables it by default for everyone with no option to turn it off. It successfully prevented my government² from decrypting user messages even with court orders.

It's a major improvement over whatever bolted-on security email has.

¹ https://whispersystems.org/blog/whatsapp-complete/

² https://www.forbes.com/sites/parmyolson/2016/05/03/whatsapp-...