Cardamom grown in cool, humid hills ripens slowly, and slow ripening builds oil in the pod. That oil is the aroma you notice when you crush a pod between your fingers.
Look for plump, green pods of an even size, and store them whole in an airtight jar away from light. Grind only what you need, just before using it.
Try one pod in your morning tea, or a pinch of fresh seeds in rice or payasam, and the difference shows up straight away.