The method of application depends mainly on the product you decided to use. If you choose thin polyurethane, your job will be somewhat simpler by using a sprayer. The main disadvantage here is that it’s the messiest solution and the one that creates the most wastage. Using a regular paintbrush will give you the most control and less wastage but it is the slowest solution. Using a roller can be a good compromise between the two. Due to this, there isn’t a clear winner on the best applicator for polyurethane as it’ll simply be the one you prefer.