It depends which one you use. Voxel models can potentially end up having high poly counts since every voxel face is equal to 2 polygons, however they're great since they be automatically deconstructed cube by cube with the right engine and coding. As for the lighting, it varies depending on what you're trying to achieve but at the base level there shouldn't be any major problems with it.
Here's a great article that explains voxel art in greater detail: