I went from a Nexus 5 to a Sony Z3 Compact and haven't looked back. The form factor is so much more convenient, I really hope more manufacturers look at it again.
My one complaint with my Z3c is actually my dock, the magnetic pedestal design sucks. I've had to RMA seveal docks form Sony just to get one that worked most of the time. And even then, the magnet disengages and the power pins drop = no charging, which is an unwelcomed surprise in the morning. I've since moved to a magnetic cable and I'm much happier.
the Z5c is pretty tempting, but I'll admit the 6s+ is also tempting. I'm growing tired of Play Services killing my battery on a whim