It is my understanding that with marines you have to build your tank up slowly and can't even add fish for 6 months or more. Then, when you do, you have to be very careful what you add and the order you add them so they will live together. Someone might want that angel very badly but is unable to get it right then due to their tank not being ready or having to move another inhabitant. Overall turnover is higher for freshwater from a livestock point of view.
Having read a lot of saltwater posts re set-up costs, running costs, and choosing inmates I am afraid I am going to have to be boring and stick with freshwater - no matter how beautiful a well set up marine tank looks