If you are going to be using wall stencils, you probably are trying to decide what type of brush to use. Stenciling needs to be done with a certain type of brush to get a good result.
Type 1: Bristle
A bristle brush designed specifically for stenciling is by far the best type of brush to use. A stencil brush needs to be very stiff and if you 'pounce' it against a hard surface the bristles shouldn't give, or give only slightly. This is important so you can control the amount of paint you are applying in the stencil. The idea of stenciling isn't to fill in the area entirely, but to create a shadow of paint that thoroughly covers the design area but doesn't leak underneath the stencil.
Bristle brushes come in different diameters so always choose a brush according to the size of the area you will be filling. The smaller the area, the smaller the brush should be.
Type 2: Foam
Foam brushes can be very good to use for stenciling. They should be only lightly loaded with paint, and then tapped several times against a paper towel to remove most of the paint in the foam. This type of brush is especially good for uneven surfaces such as cement or textured walls or ceilings.