I'd like to chime in here about why I used propane.
My preference would always be to use a wood or charcoal fire, but unless you have an actual pizza oven, it is terribly inefficient. There was a review of the Pizza Kettle insert (On Serious Eats, I believe), and it took a boatload of coals to get it to temp, not to mention the fact that it can only hold those temps for a very short period of time.
I wanted something that gave me complete control over the temp with the simple turn of a knob, that was efficient, and fuss free. You will NOT get that if you use a wood or charcoal setup in a kettle, end of story. I'm not criticizing going that route, it's just not what I wanted is all.