Azul Duel is basically a more advanced version of the original Azul for experts who have played plenty of the original game. In addition to new twists and placement bonuses (similar to Summer Pavillion), it makes the game a little bit longer and more predictable in terms of length, since it no longer ends when one player achieves a row. Ultimately I'd recommend the original Azul because it's absolutely a great 2 player game on its own, and Azul Duel only to those who have already played a lot of the original game and want more space to stretch out and pursue advanced strategies.