To me the two are not all that comparable, especially on a BTU basis. Really what is important is "how warm do I feel factor". A
rocket mass heater is superior because it takes the 26 million btu's in a cord of wood and makes you feel 26 million btu's of that wood. With a
wood stove you might feel 13 million btu's because the rest is going up the chimney.
But it takes considerable time to build a
rocket mass heater, they are fussing on their design details, they take up space in a home, and are prone to weather variations. In contrast a wood stove is ready made, already engineered out, and works by sheer volume of wood being consumed within it. Done right though, they do take up space in a home...maybe not as much as a
rocket mass heater, but it is a considerable loss to living space.
The real question is, how much wood do you have available?
For me, I live in the most heavily forested state in the nation (Maine) and have hundreds of acres of forest. It took me two days to cut the 5 cords of
firewood I need for my home this winter. Since I used a pot bellied stove, I use waste wood from my logging operations...limbs, brush and saplings, so my wood is tiny in size. I also have the forestry equipment to gather volumes quickly. Some people do not have this. So for them the better alternative is a rocket mass heater that uses less wood, and uses smaller sized wood that there area has. I have NO ISSUES with that at all. Some people fall in between these two extremes and their decision making might be harder.
So too will time and skill set. I am confident I could build a rocket mass heater, but again this is a heavily forested, cold state so used wood stoves abound. I just had one given to me, and installed it (myself) for $115. That is probably comparable to a self-built rocket mass heater. But again, it depends on the homeowner. If I was to sum it up i would say that few people would ever regret building a rocket mass heater, but for many of us, a "wood stove is efficient enough" keeps us from building them.
I hope this is a fair comparison???