Not sure if anyone could possibly use one protocol for everything however, in my case for my switches, plugs, door locks and some door/motion sensors they all are using z wave.
No specific reason why, it's mainly because I started with vera which had built in z wave so It was familiar to me when I switched over from HA.
I am currently using the Z Wave JS UI add-on, with a ZWA-2 antenna and for the most part been happy. The recent change to the ZWA-2 has helped my network A LOT. I live in a ~13,000sf home so range is big time for me, and with the new antenna the vast majority of my devices connect directly the controller. I have 59 nodes so my network isn't huge but not small.
My overall experience with Z Wave is ok though, I do tinker a lot and it's really easy to fudge something up with no apparent reason why. In my experience once you get network set and working well don't touch it. If something randomly happens (rare) it is kind of hard to troubleshoot as logs don't tell a whole lot, and my troubleshooting is usually just based on my experience with Z wave. The devices themselves are a bit more expensive than the Zigbee counterparts and I believe that has something to do with the fact that all z wave devices need to be licensed. No problem for me I do prefer to have devices that are vetted. Generally, I do see more newer devices being released with Zigbee support and not Z wave but aside from mmWave sensors I haven't really seen anything that I wanted.
I have deployed smaller scale <15 node networks at family members home and those work very well. A set it and forget it ordeal. Also could be because I don't mess with those networks after set up much 
IMO you can't go wrong between Zigbee or Z wave. I would stay away from any wifi devices though since you limited to what local control they offer, and definitely avoid, at all cost any cloud reliant devices for obvious reasons.