I would choose a Nexus 5X. Mainly because I just recently had a Nexus 6 and before that a iPhone 6 Plus and now have a Galaxy S6 and I actually like the smaller profile better than the larger. I also miss the update frequency of Nexus devices.
I think I'd go 6p, while big, I know a couple people that have one and said its amazing and the specs are better than that 5x which I've heard can be laggy at times.
6P... easily!! It's basically better in every aspect; not that the 5X isn't a great phone, too. But I say bring on the bigger screen and better specs! Yeah, baby!!
6p. Because if it breaks, it's big enough to make a good boogie board for my kids. Repurposing... And it looks like the best Android phone for me, time to retire my poor original Moto X.