I think a hardy fish is easier to care for. Feed 'em and give them fairly clean water and they're good to go. They also get you used to doing water changes and getting used to testing. Corals need good water quality, to some extent the right balance of elements like Mg, alk and Ca. Lighting is more crucial too. But that being said, there are some really easy, inexpensive corals that you could probably introduce at the same time. Why make yourself choose one over the other when you cann have both
