I really like steel 72's! I had an alum back in 1975 and it just didn't last. My oldest steels are a set of 38's that were made on 4/1943 and 5/1943 and they just passed hydro! If I went with HP it would have to be steel also. Yes they are costly, but they will last a lifetime. I've heard of welding cylinders that were from the turn of the 20th century still in use. Steel, get you some. Tim