Hi BeachBumm - I'm not as knowledgeable as many on this site, and people should correct me where I'm wrong, but I'll give you my take on why I've decided on a cast over steel design.
I have a Vermont Castings Defiant cast iron stove which is 17 years old. It came with the house I bought 7 years ago so I don't know how it was used the first 10. I use it as a 24/7 primary heater for my home. It has slowly become more difficult to control the burn in the stove. I work with a great stove shop who has provided professional repairs. The cast parts are cemented together, with time the cement slowly fails producing small air leaks. Get enough of them and you can no longer reduce the burn rate. Last winter this led to an over fire and further damage to the interior components of the stove while the air intake was fully closed down. Long story short, the stove needs to be completely disassembled, parts replaced and rebuilt and re-cemented. Total cost of the repair is greater than 50% of a new stove, so I'm getting a new one.
Steel boxes are fully welded, not cemented, which eliminates the problems I've had. My understanding is that the fire boxes are very robust and will not need much maintenance unless abused. So the steel makes sense for the box. That said, I like certain performance elements of the cast. In my opinion, it evens out the heat. It doesn't swing widely with the swings in fire temperature. It also retains heat for a long time which provides residual heat after the fire goes out. I especially like this in the shoulder seasons, I can get the stove hot to warm the room, let the fire go out and have residual heat to keep things comfortable for a while. Having the cast over steel also provides convective action to heat the air and help move the heat through the home. Add in that, in my opinion, cast looks way nicer than steel and you get the best of both worlds!
That's how I've come to my conclusion, others may have different opinions or value different performance characteristics which lead them to other designs. Now if I could just decide if I'd prefer a cat or secondary combustion stove I could pull the trigger on one!