I would suggest International Law based on my personal experience, the Constt. Law is lengthy and low scoring as well. In Constt. Law you have to cover the constitutions and constitutional bodies like Supreme court, Parliament, President, prime minister, cabinet etc of United Kingdom, United States of America, France, Former Union of Soviet Socialist Republic, Pakistan and India.
Hence you should go for International Law.
Your attitude, not your aptitude, will determine your altitude...Zig Ziglar