Although Maine puts up a good one. I think the best whole steamed lobsters I've had, were hard shell. But the real reason behind the price difference comes from the extra meat per pound in hard shells. Because the lobsters she'll is hard, it has grown into it. That means the shell is filled(or nearly so) with the lobster meat. New shells are oversized to allow the lobster to grow over the season. In the new shell state, the smaller lobster is surrounded by water in the shell(sometimes, grossly so).

When we were in the biz. hard shells had about 20% more meat per pound than new shells. So we paid about 20% more. Then we marked them up even more and told our customers, they were better.