Swimming applications its more common to see dehumidifiers, i've yet to see a Desiccant in action on a pool hall.
Low temperature drying, desiccants will perform better at lower temperatures and humidity levels than a mechanical dehumidifier. Defrosting is not required on desiccants.
Mechanical dehumidifiers add more heat to the space where as desiccants emit far less heat to space, applications requiring a constant humidity at a controlled temperature would better suit a desiccant.
No real winner here they both excel in different applications.