Leaves have a much stronger smell and of the spices used in Indian cookery have the most characteristic ‘curryish’ scent IMHO. I have taken to not using the leaves myself as the aroma can hang around for a long time. Doesn’t affect the dish’s taste to omit it that much.
That's odd because I've found the dried leaves don't seem to impart much flavour compared to seeds. Maybe I had old leaves.
Fresh leaves I use towards the end of cooking. Its well worth growing in a pot (or ground) if you have an outdoor space. My local Asian shop sells fresh leaves from time to time but I can't rely on them to have them.