Two great reviews of the new iPhones dropped in the past couple days: John Gruber's and Matthew Panzarino's. Both are thoughtful and fairly deep. And while they both touch on the software, they focus almost entirely on the hardware. Interestingly, their conclusions about the biggest (no pun intended) question about the hardware was very similar.
Regarding the size question, here's Gruber:
If you simply want a bigger iPhone, get the 4.7-inch iPhone 6. That’s what it feels like: a bigger iPhone.
If you want something bigger than an iPhone, get the 5.5-inch iPhone 6 Plus. It feels more like a new device — a hybrid device class that is bigger than an iPhone but smaller than an iPad Mini — than it feels like a bigger iPhone.
And here's Panzarino:
The iPhone 6 Plus is a great option for people who don’t have or want an iPad — or simply don’t want to carry it. Where the iPhone 6 is a great upgrade to the iPhone line, the iPhone 6 Plus is a fantastic ‘computer’.
I fall decidedly in the camp that doesn't want to carry an iPad. I've had iPads since the first one. I loved it. I've carried an iPad Mini for the past two years, and I love it ad a device. But I live on my phone. If I can get more room on my phone, I think I can give up my iPad. The idea of a new, The iPhone Plus is closer in size to a paperback than the iPad Mini is, and I'm quite comfortable reading a paperback at length. I read and send significantly more email from my iPhone than from my iPad. I more frequently use my iPhone to SSH to routers, switches, and my computers to help in troubleshooting. It seems very compelling to get more screen size, higher resolution, better battery life, and a marginally better camera all on the device I most often use, while trimming the number of devices I carry by one. When I need more oomph, I'll get my laptop out.
On the other hand, my wife doesn't have a computer, and she uses her iPad nonstop. She saw the cutouts I printed at work, and decided she wanted my 5s, and willingly offered up her upgrade. I think that's largely because she's very happy to use her iPad at home, and her iPhone while she's out of the houe. Where I "step up" to a MacBook Pro, she steps up to an iPad Mini.
I'm kind of rolling the dice. I haven't held the phone in my hand (or to my head). The closest I've gotten is holding a paper cutout that approximates the phone to my head. But, hey. Worst case scenario, I decide it was a mistake, and replace it in two years.