There are a couple of different issues.
Ideally, you want two repeaters of each protocol in each room. A mains powered sensor can act as a repeater. (Zwave repeats only for zwave, zigbee repeats only for zigbee.)
Most people don’t want to spend that much money, though. You can get away with one repeater of each protocol about every 40 feet (60 feet for Zwave plus) in a typical US home.
But if you are going to use the sensors anyway, battery-operated sensors can’t act as repeaters (in order to save battery life) while mains powered sensors can.
Additionally, a mains powered sensor can often be set to a shorter reporting interval because it doesn’t have to sleep, again, to conserve battery.
On the other hand, battery powered sensors have the option of being placed anywhere you want and can operate even if the power is off, although that’s less useful with the smartthings system since it’s primarily a cloud-based platform anyway.
So what you want to use is up to you. Different things work for different situations.