A quality paintbrush will hold more paint, drip less, minimize brush mark, and maximize accuracy. A poor quality paintbrush can make even the best paint look bad.
An angular brush will help create a straight line. The finer edge of tapered bristles also help with accuracy. Try a 2” (63mm) Angular Brush.
A high quality microfibre or lint free roller is always the best choice. After that, look to match the thickness (pile) of the roller with the sheen of the paint being applied. The shinier the finish (eg. satin, gloss), the lower the roller pile (10mm, 13mm) required. A higher pile (15mm) is better for a flat finish, as ceiling paint tends to be. A thicker roller will also hold more paint, therefore reducing the number of trips back to the tray and ensuring wet paint edges (important to avoid those frustrating dry roller marks than can occur from fast-drying ceiling paint.)