I couldn't justify the 128GB after looking at my 64GB Air 2 and seeing it over half empty. Coming from a tiny 16GB 5s has gotten me used to not filling my phone up with random crap (as I did with my 32GB iPhone 4) and now 64GB feels like more storage than I need.
I did have a hard time deciding whether to go 6S or 6S Plus, but after holding the 6 Plus I know that although I could fit it in my pants pocket, it wouldn't be comfortable. The other thing is, the whole reason I got the Apple Watch was to not have to constantly pull my phone in and out of my pocket. If I'm leaving it in my pocket then what use is the big screen?
The final nail in the 6S Plus coffin was when I heard a rumor from somebody who claimed to have spoken to an engineer at apple, and they said the OIS isn't actually a feature on the 6 Plus so much as it is a "fix" to make the 6 Plus shoot photos as good as the 6. The story on that goes; The 6 Plus is a larger phone and when you hold it to take a pic, the lens is further from your wrist on the plus, your wrist being the axis on which the aim of your camera is dependent. So, it shakes more, hence the need for OIS and the reason why Apple doesn't advertise the "Plus" as having a better camera than the 6.
So take that with a grain of salt, or put it in your pipe and smoke it. Yeah.