I would go with a sump first as it will add a greater volume of water to your whole system, it gives a place to put your unsightly things like heaters and skimmers as well as when you do water changes you don't have to disturb the DT. Thats my 2 cents worth. HTH
65 gal reef
2 PC's 192W each , 20 gal sump/fuge
4 false clowns, 2 firefish, cardinal, midas blennie, toadstool, zoos, shrooms, trumpet coral, torch, pagoda, frogspawn, poylps, red open brain, devils hand, hermits, snails, 3 cleaner shrimp, coral banded and a emerald crab.