RBA = Rebuildable Atomizer (covers Tanks and drippers)
RTA = Rebuildable Tank Atomizer
RDA = Rebuildable Drip Atomizer
RTA's are more convenient if you are out and about and there a very few that are close to the flavor of RDA's. RDA's less convenient to go out and about but are great for flavor, clouds, and testing different e-juices without committing a large volume of e-juice.