The primary feature of messaging software is &quot;all my friends are on it&quot;.  As an ex-Googler, all my friends are on Hangouts.<p>I think that on a technical level, WhatsApp is the best messaging software on the market.  It at least features reliable message delivery, something that both Hangouts and iMessage have yet to get down.  But its usage is largely limited to my Indian friends here in the U.S, which makes it of limited use to me.