If it was me, I'd go for the Emperor. You get two fish in one with the change in colour! However, what should be more important to the decision is 1) how big your tank is (which may mean to pass on both; and 1) which is healthier? If there are any signs/indications of disease/faded colours etc, I would pass on the fish. Also keep in mind that as this fish grow then can become quite the bullies - not mention potential issues with consuming reef inhabitants. So, if you have something in your tank now that your really like, make sure it (and the system) would be compatible with a large Angel.