I'd choose the 6P, because I would want to try out a larger Android phone and see if it might be something for me now that I am stuck with a 2012 Samsung Tab 2 Plus (too big for my taste)
I'd choose a Nexus 6P since I'd like the additional screen real estate. Also, it'd be nice to have a phone with the premium build quality and feel so I can show my iPhone friends what a real phone is like.
I'd love to win a Nexus 6P because of that pure Google experience. I had a N4 and it was amazing how stupidly easy it was to root it and get it to how I wanted it to look like. Plus that 6P camera...! I'm honestly just so excited that people are finally giving Huawei the chance it deserves to be taken seriously.
I would choose the 6P because I switched from the Moto X 2nd Gen to the MXPE and really enjoy the size despite thinking I wouldn't. Using smaller phones has now become awkward. Go figure.