Each of the islands is different.
Formentera has fine beaches, but is low lying and rather bleak to my way of thinking.
Ibiza is hilly, rather than mountainous. The hills are all covered in pine trees, and the plains inland have olive groves baring the red-brown earth. The SW coast boast very high cliffs, and the dramatic, apparently unclimbable Isla Vedra. The north coast has cliffs all the way.
SW Mallorca and the north coast is mountainous, and the cliffs rise up to 300m. The SE coast is lower lying, with gentle hills inland, and indendented with dozens of lovely calas. The Bay of Palma has cliffs, but built of concrete - best in my opinion to sail by well offshore! Inland, the northern third of the island is mountainous, with many lovely, unspoiled towns and villages. The southern two thirds is relatively flat, with a fair amount of industry.
Menorca also has a hilly northern half and flatter southern. From the sea, the NW corner appears bleak, with the rest of the north coast having low cliffs with lovely vistas into the valleys. The south coast is rather featureless from offshore, but there are dozens of attractive calas indendented into the low cliffs. Inland, Menorca is reminiscent of areas in England, with many tiny fields marked by dry walls, and used mainly for grazing cattle.