What type of salt is more effective for melting ice

Sodium chloride is used for ice cream makers because it's inexpensive, readily available, and non-toxic.

OR

Rock salt has been a staple in the ice-melting industry for a long time and is still very popular for use at home and by public utilities

Potassium chloride, rock salt, magnesium chloride and calcium chloride are the most common ice-melting salts used today. Ice melters are not naturally hot; they do not melt ice as the term suggests, but rather, they act to depress or lower the freezing point of the snow or ice they are spread on. This allows the salt or chemical particles to bore their way through ice and form a layer of brine under the surface, which helps the top layer of ice break up. If the brine is able to remain in place, it will continue to melt any snow or ice that comes in contact with it.