I went from a 5s to 6s and I'm not crazy about the bigger screen. A lot of times I find myself fumbling to reach a screen element with my thumb (yes, I know about Reachability). I use 3d touch intermittently, but not enough that I can't live without it. I would actually consider "downgrading" to this phone if the specs are decent.
I "downgraded" from my 6 that I was using for ~11 months to a 5S about 2 months ago. Love having the 4" back.