Which is more powerful ambien or lunesta (eszopiclone)?

Neither: Zolpidem (Ambien) and eszopiclone (Lunesta) are medications used on a short-term basis for insomnia. Both act at the benzodiazepine receptor although they are not chemically in the benzodiazepine class. They are generally useful for early insomnia (getting to sleep). Neither is more "powerful", but effect depends on dose, and sometimes one works for a patient and the other doesn't.