IDY and CY (compressed yeast) are closer together than CY and ADY. While IDY also has its share of damaged yeast cells due to the drying process, the issue has been addressed through the addition of a small amount of ascorbic acid to the dry yeast, while the ADY (active dry yeast) has not had any ascorbic acid added, so the doughs made with ADY actually end up slightly softer than when made with IDY. The biggest problem that we have seen is with conversion of one type of yeast to another. When used at correct conversion levels, there is no difference in finished product flavor between IDY, ADY, or CY. The trick here is in using the CORRECT conversion, and the conversion recommended by the manufacturer, may not always be the correct one for your particular dough formula. For bread makers, the correct conversion level is the one that provides the same final proof time as the yeast type being replaced. For pizza makers, I like to use a plastic glass or cup, oil the inside and place a weighed amount of dough into the cup/glass, flatten the top so it is as even as possible, lightly cover with a piece of foil and set aside to proof/rise until the dough reaches the top edge of the glass/cup, then record the time required for the dough to rise to that height, now, replace the yeast with the type you want to use, and repeat, adjust the yeast level until the time needed for the dough to rise to the top edge is the same as with your original yeast. Now, divide the new yeast level by the original yeast level and you will have the correct conversion for your specific dough.
Tom Lehmann/The Dough Doctor