Better is to spray stain on a fence as compared with roller because roller for this project is extremely time consuming and as well labor intensive.
If the area is small, then you can use it to save your money for a bigger area of yard around the house recommended spray.
Using a sprayer, apply the paint quickly to the surface and use a brush and roller to push it into the wood.
If you are interested in using a sprayer, most recommend using an airless sprayer when applying wood fence stain and as well check Best Paint Sprayer For Fence Stain.