Nexus 5x and very happy with it for now. Having gone down both the value and flagship routes over the years, I'd be unlikely to spend more than $300 on a device ever again, and that would be mostly for a better camera.
I predict were hitting a wall with mobile devices, much like we did with pcs just over 10 years back - what we have is good enough, and $200 devices are offering most customers pretty much everything they need in a smartphone. The hardcore crowd will always command a small but valuable market, but I can see the market becoming a lot less lucrative for a number of brands over the next couple of years.