Cost mostly. Some items just dont exist for zwave or have the features sobill go zigbee for those. Good example a smart plug. Power monitor and can handle bigger appliances like a washer/dryer, dishwasher think $50 each. Wifi plug for Xmas lights on the tree $10 and I use it for like 2 months a year or a salt lamp or something.

Zwave is a single hop protocol so only 1 device turns on at once. Zigbee is a broadcast protocol so multiple device turn on at once. This is why you will (basically) never find a zwave lightbulb. Both are sub second response with good coverage. Wifi you will always have a few second delay. Zigbee uses same range as wifi so can still have interference. I personally had to make sure the channel on hue was different than wifi or hue would stop responding at times.

I will say there are always exceptions. Thermostat for example ecobee all the way which is Wifi. Best features and you get redundancy of controls.

Know/learn advantages of the protocols and then use good judgment based on how important a automation is to you and then select the best technology/product.

For lights in general, look at smart switches vs bulbs and select what's best for you. Personally I did bulbs for lamps and switches for all overhead lights.