Comparative:
* Emptier: This is the regular comparative form, but it's not always the most natural choice.
* More empty: A more common and flexible option.
* Vacanter: This implies more emptiness in terms of space or occupancy.
* Hollower: This implies a deeper sense of emptiness.
Superlative:
* Emptiest: This is the regular superlative form.
* Most empty: A more common and flexible option.
* Vacantest: The most empty in terms of space or occupancy.
* Hollowest: The most empty in a profound or metaphorical sense.
The best choice depends on the context and the specific meaning you want to convey.