According to the folks at Baking 911
, to substitute Instant yeast for Active Dry yeast:
BY WEIGHT: Use 2/3 (0.67) as much Instant as Active Dry.
BY VOLUME: For 1 teaspoon Active Dry use 3/4 teaspoon Instant.
So ... to replace 2 packages of Active Dry Yeast (2 1/4 teaspoons each) you would use just a smidge over 3 1/3 teaspoons of Instant Yeast. (4.5 teaspoons X 0.75 = 3.375 teaspoons)
I don't know that instant yeast is better - it just doesn't have to be "proofed" before being used - that saves time in a bakery. Bread machine yeast is also instant yeast.