If you're considering the material:
* Brick: A common alternative to stucco for building exteriors.
* Stone: Another popular material for building facades.
* Wood: While not as common for exterior walls, wood siding is an option.
* Concrete: Can be used as a smooth finish, but differs in texture and application from stucco.
If you're considering the texture:
* Smooth: The opposite of the textured finish of stucco.
* Rough: While not the opposite, this describes a contrasting texture to the typically smooth finish of stucco.
If you're considering the application:
* Paint: A completely different way to finish a wall surface.
* Wallpaper: Another alternative to covering a wall with a decorative material.
Ultimately, the best antonym depends on what specific aspect of stucco you want to contrast.