Brushing is better for cutting in and smaller tasks that require more precision. Choose no-loss brushes like this Harris Premier Set. They lose fewer bristles and spread the paint more evenly.  When using a roller, choose the correct roller cover. Rollers cover more ground and leave a neater finish. Foam naps give good coverage but leave tiny air bubbles. Wool blend sleeves spread the paint better over larger areas, but they shed fibres.