Sandblasting

Sand is best for heavy duty removal, especially on harder metals like steel or cast iron. If you are using sand on sheet metal, then be careful of the heat build up leading to warping. Beads are good for most other things, is more gentle. May need more time to remove more stubborn stuff. Beads are better on aluminum, and since more gentle, is good for a general "clean-up" and "polishing" of parts without removing the original finish like galvanize.