There was no premium in my area for concrete so that is what we have. From what I've seen Vinyl covered stairs often don't fit right no matter if the structure underneath is concrete, steel or polymer. Also I don't like how slippery vinyl stairs are. For that reason we went with molded stairs (some may not like that look).
Liner fit around the rest of our concrete walled pool is flawless, but concrete is what our pool builder does primarily.