There are dozens, even hundreds, of smartphone models to choose from. But in reality your choices are not so many. Only five smartphones matter to professional and business users.
They're all the flagship models from the flagship manufacturers, which means they have sufficient horsepower and memory, high-quality screens, and the essential interaction hardware (fingerprint scanner, cameras, ambient light detector, LTE radio, Wi-Fi Direct radio, NFC radio, Bluetooth Low Energy radio, high-capacity battery, and so on) to go beyond making calls and sending texts and instead to run real apps and services. They're updated on fairly regular schedules each year. Plus, they have the market power to attract attention and sustain carrier relationships.
You might go for an older model or for their cheaper, less-capable versions (like the iPhone 5c or Galaxy Core) for your kids or casual-use relatives, or if you want a basic personal smartphone in addition to your business smartphone. But most professionals will get one of these five, in descending order of quality.
The current model is the iPhone 6 or its larger iPhone 6 Plus variant, for those who want a mini-tablet in their pockets. The new model introduced each fall becomes the it smartphone for the Apple community, and in the United States for about half the populace.
For good reason: Apple still delivers the best overall experience, and each year's flagship model is the best showcase for that experience.
Samsung Galaxy S
The current model is the Galaxy S6 or its curved-side Galaxy S6 Edge variant. Samsung has gone up and down in the quality of its Android flagship; the S III and S 4 were solid, the S5 cheap, and the S6 lustrous. Even when Samsung stumbles in its new editions, the Galaxy S remains the best experience in the Samsung universe -- which usually means the best Android experience, period.
Samsung Galaxy Note
The current model is the Galaxy Note 4, the original stylus-equipped phablet for those who want a mini-tablet in their pockets. The Galaxy Note is more than a bigger version of the Galaxy S (as the iPhone 6 Plus is of the iPhone 6), thanks to its stylus and intentional tablet PC-like design. The Note is not for most people, but it's beloved by its users.
The current model is the LG G4. It's a sleekly designed smartphone with good hardware, though so-so battery life. The primary appeal of the LG G series is that it's not from Samsung, making it the un-Galaxy option for Android users. Of the not-from-Samsung Android options, the LG G series has been a consistently good alternative.
Microsoft Lumia 830
Few people use Windows Phone, though it does decently in some countries. If you use a Windows Phone, you can reliably get compatible smartphones from only one company: Microsoft, which bought Nokia's smartphone business last year.
Most of the Lumia line is composed of inexpensive, compromised devices. The year-old Lumia 830 is the exception, providing hardware quality comparable to the better (though not the best) Android smartphones or an older iPhone. For Windows Phone users, it's the only smartphone model that matters.
Microsoft is hoping Windows 10 will reinvigorate the Windows Phone platform, and I'm hoping that, if successful, Microsoft will then reinvigorate the hardware to run it. If you can, wait to see if Microsoft comes up with a business-class device. In the meantime, your viable choices are the Lumia 830 or the more-available but less capable Lumia 640.