Which of these is a suitable material for waterproofing interior walls?
A bathroom should have water resistant materials in the places likely to be splashed with water. Stanard drywall is not used in those locations, but rather hardboard or cement board should have been used. If the proper materials were used in the first place, then you can just prime and paint over them. 

What @Ecnerwal is saying in his comment applies more to a situation like basement wall waterproofing. In @Faheem's situation, the water would be coming from the interior, so it would not cause the waterproofing to peel. However, in a properly constructed bathroom, no additional waterproofing coating is required. You may wish to use a "kitchen and bath" paint, but beyond that there's nothing more needed.