Brushes and Rollers
But, wouldn't you know it, brushes and rollers come in a bewildering array of sizes, materials and types. Which is best for the job? The answer to that question depends, of course, on the job being done.
Brushes
There are two basic types of brushes: natural bristle and synthetic. Natural bristle brushes tend to be a little more expensive, but this is one area where it's unwise to try to save a few dollars. The ultimate result will be determined, in part, by the quality of the tools you use. Natural bristle brushes are perfect for oil-based or alkyd type paints. They're not generally recommended for latex paints, since they absorb too much water, leaving the paint dryer. That makes the paint spread less evenly. They may not last as long as synthetic. Though some will last longer, compared to cheap synthetics. But they'll provide a smooth, even look that is easy to generate. Still, a quality synthetic brush definitely has its uses. Latex can be applied with natural or synthetic, where they do an about equally good job. Some can be used with alkyds as well.
In either case, ensure that you get a quality brush of the right size. A brush with split ends may look ragged and used. But it's the perfect tool for evenly spreading paint. A much finer surface can be more easily created using a split end. Paint tends to lodge between the split, where it's dragged over the surface much more smoothly and evenly.
For most jobs you'll want a brush that is about 50% longer than it is wide. So, a 2 inch wide brush will need to be at least 3 inches long. That saves on hand fatigue, provides enough flex and helps create a smooth texture. If you really need to cover a lot of area quickly, use a roller instead.
Rollers
Like brushes, rollers come in natural material or synthetic. The same considerations apply to rollers as to brushes, with a few additions. The nap of a roller determines to a high degree the final texture left behind. A long, rough nap creates a rougher look. That may be just what you want. But if you want the smoothest possible surface, get a very fine, low nap.
Smooth plaster requires a nap of 1/8-1/4 inch at most. For a rougher texture, 3/8-1/2 inch is ok. Make sure you get a roller that 'bounces back' to its original shape when squeezed. That happens inevitably when the roller is moved over the surface. Here again, quality counts and saving a few dollars for cheap rollers is self-defeating.
The percentage of the total painting costs required for brushes and rollers is very small. You didn't skimp on the paint. Apply the same principle to the tools used to apply it. Go with the best and you'll save time and create the best possible result.