What is the order of rel subs?

I am confused in what order do the rels follow?
Does each model present different amp power and different size driver? Or are there other differences as in equalization and crossovers and microphone for set up? How is the storm different from the strata and stadium and stampede and stentor? I am looking for something that will be musical and light what I mean is not noticeable and I would like it to go low and to fill the room. Do I stick with these models or should I consider the new b series. thanks