Steel is quieter, and less prone to damage from scrapes from mufflers/exhaust pipes, etc. By using a smaller diameter the balance seems to be better long term, and less harmonic vibration, especially for a truck. I had lots of problems with my aluminum driveshaft in my F-150. It wanted to flex as hit different rpms. It was huge, also at 4". Unless you alsolutely need to save the weight, I would suggest a steel driveshaft for long term usage. Joe-JDC