If you aren't sure which one to use, these tips should help you. The first thing you should remember is to look for quality. A good paintbrush has flagged or uneven bristles, which means the brush holds more paint, and delivers it evenly. It will also have a nice tight brush and will bend easily when you push the bristles to either side. For water-based paint, you want a brush with synthetic bristles.
Oil based paints, on the other hand, require a natural bristle brush.
It's made of hog's hair or horse hair, and can stand up to the strong chemicals required to clean it. There are different kinds of brushes for different jobs. A wall brush is usually about four inches wide, and is designed to make large, even strokes. Finally, a sash brush has a slanted tip, and is just what you need to paint windows. The slant makes easy strokes around corners with little mess.