three completely different devices. do you care about size, about price, about materials used, about battery options, about whether all available
batteries for the unit fit snuggly in the
device, about immediate availability, about venting, about the use of different native or proprietary adapters for different atomizers, do you care about switch location, whether it's a mechanical or electrical device, whether the device has a lockable switch, etc.
you've named three devices, by three solid companies, but each is different and for different reasons. determining what your criteria is for the mod you want will help field the best responses, and ultimately help you make the best decision.