The comparison of the cell organelles and the most important organelle:
Plasma membrane is a semi permeable membrane that protects the cell and its components whereas the other cellular structures such as the mitochondria , nucleus, Endomembrane structure etc, each of it has its own function.
Each of the cell organelle is unique and have a special function but in spite of that all cells contain plasma membrane that protects all the other organelles from foreign substance. Hence plasma membrane is the most important membrane of a cell.