Painted trailers are the lowest-cost option for freshwater use and can be more visually appealing than galvanized trailers. In some cases, they will match the boat's color.
Galvanized trailers are suited for saltwater use as they offer extreme corrosion resistance. All surfaces of the trailer are coated (inside and out), as opposed to just exterior painted surfaces. Galvanizing will dull over time and may not be as visually appealing as painted or aluminum trailers. Galvanized trailers are a higher-cost option than painted trailers, but they will always tend to last longer under normal conditions.
Aluminum trailers are suited for saltwater use as they offer extreme corrosion resistance. They are much lighter than their painted or galvanized counterparts, reducing the overall load on the tow vehicle. In terms of appearance, aluminum is very appealing from the date of purchase and for years to come. In most cases, aluminum trailers are the highest-cost option.