Very generally, NYU is ranked as having the best Int'l law program in the country, however, HYS all have comparable, niche programs. HLS for example, has a joint JD/LLM with Cambridge University and specializes in human rights law on an international scale. YLS has a very strong theoretical program for international law, although I don't know what specialty. And SLS has great Int'l programs specializing in U.S.-Asian relations. Realistically though, your choice of type of int'l law, national region, type of firm sought, etc... will really define what is best for you.