For the smoothest and most flawless finish, a microfiber roller is your best friend! It is perfect for for a brush stroke free finish on long flat surfaces. I love using a roller for larger sized projects with flat surfaces like table tops or kitchen cabinets and then I get into any of the smaller areas with the angled synthetic brush.
Rollers sold individually or in a box of 10. Roller with frame available separately.
My top tip is applying paint first with a roller, and then immediately a few seconds after, taking a brush and running along the surface to smooth out any stippling. Sometimes rollers can leave a slight texture behind. Here’s a video showing that technique.