Your question is too vague. Sit down? Take out? Bakery? Counter service? Restaurant? Casual or part of a tasting menu/prix fixe? Need a dessert tasting menu? Afternoon? Dinner? Late night? Price point? Traditional or nouveau?
Best chocolate chip cookies
Best chocolate ice cream
Best hot chocolate
Manhattan chocolate tour
I would also look into the chocolate desserts at Jean-Georges, Chikalicious, Chikalicious Dessert Bar, WD-50, Tailor, Blue Ribbon Brasserie or Blue Ribbon Bakery, Payard, Dessert Truck, Kyotofu, Bouchon Bakery. Stay away from Max Brenner.