Universal detector means it is useful to detect the most of the compounds like refractive index detector based on their physical property. Bulk property detector means not specific to solute but sometimes its useful to solvent detection.

ELSD and RI detection are the usual ones. They are most often used with molecules like carboydrates that do not have a chromophore (cannot see by UV) and do not ionize well (cannot see by MS).

ELSD is nice because, unlike UV and MS, the response is the same for all molecules and is proportional to mass. It shows the "truth" of the relative amounts of different components in a sample. But its not as sensitive.