Z-Wave more often than not, is far more reliable.

Zigbee is using 2.4GHz. Add 50 Zigbee devices and watch all 2.4GHz connections in your home suffer (WiFi, Bluetooth, wireless mice/keyboards/gamepads...).

Z-Wave is using 800MHz range. Add 100 Z-Wave devices and watch your Z-Wave network getting stronger and stronger while all your other 2.4GHz devices continue to work as normal.

There is a downside of being an open protocol: no certification. Zigbee vendors are free to mandate the use of their hub (and software, and spying) because there is no gatekeeper. And most certainly do. Philips attempted to do this somewhat recently, only backpedaling due to the bad PR this caught them.

Z-wave devices are guaranteed to work with any hub. That means that it, ironically, behaves in a more open manner. I consider that worth the difference in cost.