There is lot more to paints than just covering up the walls. They can help you hide imperfections on your walls and ceilings. Various paints can result in various effects on your walls. If you are trying to hide imperfections on your walls, you should use a low sheen paint that is it must contain a low amount of gloss. This type of paint hides any defects on the surface of the wall. Whereas a high-gloss paint shows everything like a mirror.
The low sheen answer is a very excellent one, for small imperfections, if your walls are white like mine, (I learned this from my mother) white-out is an inexpensive answer (so you don't have to get more paint than you need)
Have you considered doing a faux treatment? I bought a rag roller, that made a fabulous effect! There are all different kinds of fun easy treatments. My wall was kinda big, so I bought a specialized roller, to do it evenly. I took a free video series from expertvillage.com. My wall had a lot of "orange peeling" going on. Now, it looks like marble.