What the "best product" is, is so completely subjective and since when did that matter anyway? You probably think that Macs are the best computer...why aren't those the biggest in the enterprise space?
In the enterprise space, BlackBerry was the "best product" because it was manageable, easy to configure, easy to encrypt and reliable for it's purpose -- making phone calls and email.
As the iPhone and Android devices became popular, users started expecting a rich web and app experience that BlackBerry just couldn't deliver -- but IT guys like me still pushed BlackBerries, because the new devices weren't managable.
Then, that changed. iPhones can be managed, encrypted, etc by an IT department with little fuss. Androids can be too, but it's more complex -- I need to buy a 3rd party app to encrypt email, and keep up with the various features of 8 different vendors and 30 different phones. So, if I buy Android devices, I need to deal with the carnival of device choices that confuses users and increases the likelihood that my people will screw something up. Or I can buy an iPhone, which costs the same or less than the Android deivce, and everyone is happy.
Sounds like the "best" choice to me.
RE: The Mac -- I am a Mac user personally, but wouldn't buy them in a medium or large business. Why? Three reasons: Macs don't have a mature (where mature == working) integration with authentication and authorization services (ie. AD or LDAP/Kerberos). Apple is a single-source, mercurial supplier. All business apps work on Windows -- 10% work on Mac.
Rhetorical question, but here's the actual answer:
None of the reasons that had hindered Macs on the uss-enterprise apply to iPhones. It's compatible with common network and mail systems, there's management software, it has the biggest application & developer base, and the (huge) profit margins are hidden in the carrier bills.
You'll find plenty of users who think otherwise and it is not worth the time to argue over which bit of anecdotal evidence or which opinion is correct.