For my money, KNX>Zwave>Zigbee. Zigbee's standard are not certified so you get non compliant devices that don't work well, and 2.4 is a very crowded frequency with lots of interference not only from other wireless devices but also microwaves, etc. Zwave solves both of these issues and generally has a higher level of quality, but for me a wired standard will always beat a wireless one if I'm starting from scratch.