While brass is an excellent general-purpose metal you can use in a broad range of plumbing jobs, stainless steel has other applications that might make it the superior choice instead. For one, stainless steel valves are much better in terms of corrosion resistance
Steel valves are durable. Stainless steel valves are especially tough because they are made of steel and because of their corrosion resistance. Steel valves can handle both high and very low temperatures. Steel valves are usually rated for a broader range of operating temperatures than brass or plastic valves.