The really nice ones :) Concrete is a lot quieter. They’ve put up several new complexes in my area, and even for $600k, you get just framed party walls. Some of the builders go so far as to build little brick extensions on the exterior facade, so it looks like masonry wall extends between the units. My unit has a daylight basement, and the below-grade party wall is cinderblock, like the below-grade exterior wall, but that ends at grade.