All of the above, but if you have to narrow it down, from Belfast take the causeway coastal road towards Carrickfergus, continue to Larne, and follow the coast. When you get to Cushendun take the Torr road (a must) There is also a nice short detour off this road to Murlough Bay (signposted)-a good spot to camp, you have to come back the same way to re join the Torr Road.
Continue towards Ballycastle and onto Carrick-a rede and Ballintoy (nice harbour and cafe). About a couple of miles further on is Whitepark Bay-a great beach. Continuing on you have the Giants Causeway (don't rate it myself, but everyone to their own), then Bushmills village-nice spot with the whisky distillery-nice shop bar and cafe. Next is Portrush, nice beaches and highly recommend Cafe 55 for a food stop. You could then turn south and take in Ballymoney and back to Belfast over the Glens