ive heard form many that pink tails are suposedly reef safe. and i have seen a few nigers in reefs without incedent.
tobys probably are you best bet, not only with eating corals, but size wise. a large 18" porky would be pretty bulky in a reef. lol. but like all puffers with anythign else, some will eat corals, others wont. i had some xenia in my fowlr to see if mine would and he never even looked at it. he also wont touch anythign but food i feed him. so he is a good one, but i know others who have just tore reefs apart, esspecialy small crustaceans.