I have (and sell) the big trailer smokers. I use a combination of wood and lump when I first start it up, but as I'm cooking through the night, I use mainly wood. If I need to get more heat in the chamber, I will add some lump, but mostly we just use wood through the cook.
Now as far as what type of wood, right now we are using pecan & almond, but grape, apple, olive and cherry are all good to use, but hard to find.