A good container should not only leave a good amount of room for Haworthia roots to elongate but also reduce the chance that excess water resides under roots. It is recommended to use containers that are ~20% deeper than roots.
A container made of a porous material (for example, clay-based unglazed ceramics) evaporates a large amount of water through the sides. It fits a humid climate better as the deeper growing medium can dry faster. By contrast in a dry climate, non-porous materials like plastic can help keep the moisture in the growing medium longer so that fine roots are less likely to dry up between waterings.