See this FAQ on Zigbee vs Zwave. Zigbee dominates the smart bulb market (both Philips Hues and GE links are zigbee), but Zwave switches with dumb bulbs may be cheaper.
I don’t know of any reason why you’d choose zigbee over zwave for locks in the US, or vice versa, same pluses and minuses with both. If you live in Australia, zigbee gives you more choices, not many zwave locks made for that market.
Most big home automation companies are using zigbee locks, but that’s because of the advantages of zigbee sensors, not the locks themselves. Since SmartThings allows for both protocols, you can choose zigbee sensors and still have a zwave lock if you like.
Within the SmartThings community, I think more people have zwave locks, they work well.