Fresh herbs are always preferable to dried ones.
Although in most cases fresh herbs trump dried (dried herbs tended to taste “dusty” and “stale” while fresh herbs tasted “clean” and “bright” in our taste tests), there are a few instances in which dried herbs are desirable, mainly in recipes involving fairly long cooking times (20 minutes plus) and a good amount of moisture. This is useful to know, given that dried herbs are a lot less expensive than fresh, and are generally more readily available.
In our tasting, chili stood out as the one dish that was better than made with a dried herb (oregano) than with fresh. Dried rosemary, sage, and thyme also fared reasonably well.
Tarragon and dill had slightly muted flavors in their dried forms. More delicately flavored herbs (basil, chives, and parsley) seemed to have lost most of their flavor when dried; we preferred fresh forms of these herbs in every test.
Bottom line? In a long-cooked dish, dried versions of strongly flavored herbs can be more effective than fresh.