Xavier Aptitude Test 2012 Paper

Ram, a farmer, managed to grow shaped-watermelons inside glass cases of different shapes. The shapes he used were a perfect cube, hemispherical, cuboid, cylindrical along with the normal spherical shaped watermelons. Thickness of the skin was same for all the shapes. Each of the glass cases was so designed that the total volume and the weight of all the watermelons would be equal irrespective of the shape.
A customer wants to buy watermelon for making juice, for which the skin of the watermelon has to be peeled off and therefore is a waste.
Which shape should the customer buy?