Some feel the flavor is enhanced with a smaller rig. We find that is a myth, but we do like having a nice small rig to hold in your hand while doing dabs rather than a big giant bong. Really whatever you like is what is best for you.
With the bomb in dab rigs we feel they got smaller as the people making them can not hold large pieces of glass. It can be much for taxing on your body if you make larger rigs both in the amount of heat you will have to endure, as well as the muscles required to hold the glass.