While “RBA” is a shortened form of the word “rebuildable atomizer,” “RDA” is a shortened form of the word “rebuildable dripping atomizer.” In short, an RBA has a tank for storing excess e-liquid while an RDA does not have such one. You may consequently have to put e-liquid to an RDA more often.
The compromise is that you’ll experience less restricted airflow. The cost is almost the same. Eventually, using an RBA will save you money compared to using an ordinary atomizer or cartomizer. This is because you only need to buy the hardware one time; after that, you can purchase wicks and wires in bulk — and a single roll of wire is enough for wrapping many, many coils.
Even if you do not decide to build a rig for sub-ohm vaping, RBAs can also benefit you due to the sheer variety possible in wrapping your own coils. When you wrap a coil, you need to choose the gauge of the wire used, the space between coil wraps, and the number of complete coils and etc.
But as the time passes, you’ll become accustomed to the differences between wrapping techniques and will find your own suitable e-smoking setup. You’ll never have to be concerned about variations from one atomizer or cartomizer to the next, because you won’t be using a mass-produced product — you’ll be using something unique you opted for and tested yourself.