I rendered a pretty swift decision myself. The 6S Plus wins. The 6P is going back.
What I liked and didn't like about the 6P sort of surprised me.
I thought I wouldn't like the fingerprint scanner placement, but I LOVE it. I wish the iPhone had a sensor built into that Apple on the back. It really works incredibly well.
What I didn't like mostly was the screen. I didn't like how saturated it was. It was saturated in a pretty unpleasant way to my eyes. I've owned Samsung phones, so I know the AMOLED deal, but this was different. In the Google Keep app for example, the colors were retina searing. Lol. After hunting to turn on the hidden settings, I found the sRGB mode switch, but that muted the colors terribly to an opposite extreme. I find it very hard to leave the color style and balance of the iPhone I guess now that I've gotten used to that. The brightness was also way less than the iPhone. It was sunset when I was trying them out. I got a nice big strong direct ray of sun to give me a worst case. The 6P nearly washed right out. The 6S Plus hung in there though some tilting was needed to minimize the glare.
I remembered quickly how much I dislike onscreen soft buttons. I hate that they swallow up the screen. I hate that they push the keyboard up higher. I think Samsung has it right in the way they persist with the physical buttons, and Apple makes surprisingly good use of the one button they give you.
I don't like how the power and volume keys are all together. I'd probably adapt to it over time, but I felt the volume buttons were just too low, and I often hit the volume when trying to power off or vice versa.
I didn't like that the battery percentage was sort of illegible. The iPhone is clear and readable from 4 feet away.
The speakers were a little disappointing to me. They were a little more full sounding than the one on my 6S Plus, but not by much. They also weren't particularly loud. I'd say the max volume was nearly even with my 6S Plus, though my iPhones tends to distort a little on the last click. The 6P wasn't exactly crystal clear at max volume either though.
I didn't give it a full on multi-day test because the screen colors and lack of brightness was a deal breaker for me.
I also sort of discovered that I really don't care for Android anymore. That's odd for me to say because I was once an Android and custom ROM junky.
All in all though, it's a real solid phone, feels great in the hand, definitely very fluid, looks great, just not for me.
I'm glad I did it because I feel even more confident that the 6S Plus was the right choice for me this year (and hopefully will remain with me for at least 2).