After having used several different kamados, I can't agree that that the quality of cooking varies much if any between the models. I have the bottom of the line Char-Griller Akorn kamado and two Kamado Joe ceramic kamados (Classic and Big Joe.)
The Big Steel Keg is a much better smoker than the Akorn because it's more air tight and a lot easier to control the temperature. The Big Green Egg is going to be just as easy to control the temps. The BSK has one advantage over the ceramic kamados. It's easier to bring the temperature down in that system because there isn't nearly as much heat being retained in the body of the grill. It's also a lot lighter and easier to move around if you want to take it somewhere with you.
I have no experience with pellet grills...