Daniel Miessler asked himself which iPhone 6 to get and I did the same. Here are my thoughts.
First, whether considering the 6 or 6 Plus, there is definitely a decrease in pocketability. But I see the move to larger screens as necessary  as we use the devices we call phones more and more as computers-which-you-carry-in-your-pocket. 
After Apple’s keynote, I hesitated a little bit between the iPhone 6 and the 6 Plus. Initially I was pretty sure that I wanted the larger size. Then I printed the templates and realized that the Plus was larger than I had expected. I started having doubts about whether I would like the larger device, in particular:
- Will it fit in a pocket relatively comfortably, or will it be a constant annoyance? 
- Will I be able to use it with a single hand at least part of the time? 
In the end I decided to get the 6 Plus and to consider it an experiment: a device so different from the ones I have had so far (iPhone 3G,  iPhone 4, iPhone 5) might change my habits in some interesting ways.
I am also experimenting in another way: I have had AT&T contracts since the iPhone 3G in 2008. This time around I ordered an unlocked iPhone 6 Plus for use on the T-Mobile network.  I like the idea of having an unlocked device, as well as having more options for plans. I will probably try to get one of the T-Mobile prepaid plans (which they don’t advertise much). 
Here are the features specific to the 6 Plus I am looking forward to:
Improved camera with optical stabilization. I have kids and I consider the camera which I carry with me at all times important. 
Bigger screen. Many activities should be more comfortable with a larger screen. Will I use my phone for reading more? Will I still be interested in getting the next Kindle?
Improved battery life. Depending on which feature you are looking at, the battery life is supposed to be better across the board. For example, Wi-Fi browsing is 10 % longer and standby 60 % longer.
I am also looking forward to the following features shared by the 6 and 6 Plus:
Improved speed. The CPU improvement announced is “only” 25% over the iPhone 5S, but the 5S was about twice faster than the 5, so that will be a nice improvement.
The new hardware design. I like the rounded body, which looks more like the original iPhone and should make the device pleasant to hold. The iPhone 3G, while plasticky, was also great to hold due to the curve of its back, and from this perspective the iPhone 4 to iPhone 5S design was a step back.
Apple Pay. I don’t need to pay in stores all day long, and this won’t revolutionize payments,  but I am intrigued by this combination of Touch ID and NFC. Will it work as reliably and fast? Will it work in stores I am likely to visit? The US is finally implementing “Chip and PIN” cards to help prevent fraud. This means that it might become a little slower to pay with cards than it has been so far, as you will have to enter your PIN.  Could Apple Pay be slightly more interesting due to this move?
I am looking forward to retire my beat up iPhone 5!
We can say it now that Apple is finally in the race! ↩
I already knew the price of the device, but it was still a bit of a shock to see the final price in the shopping cart (almost $1,000 with sales tax!). It is a neat trick that the big US carriers have pulled to subsidize the price of devices over 18–24 months. I would bet that a large majority of smartphone users do not know the actual price of the device. ↩
I don’t have an absolute guarantee that this will work out. But the phone will be unlocked and T-Mobile has a “bring your own device” option so I am hoping things will be smooth. ↩
The camera of my iPhone 5 has gathered dust inside, and I find myself reaching for my wife’s iPhone 5S regularly. I also take my SLR on specific occasions. ↩
For two reasons: because the major credit card companies are still involved, and because the system is limited to the Apple ecosystem. ↩