Anything you'll feel confident wearing. Those who have never worn a hat before tend to start with something short to medium, around 2.5 inches or shorter. Our Dean the Butcher is a popular choice for this reason. Once you get comfortable with that, it'll be easy for you to decide to go up or down in brim size. Otherwise, the best trick is to wear a hat that sits within your frame. If you have narrow shoulders, try a short-to-medium brim; if you have wide shoulders, a wide brim may suit you best to fill out your frame.