Almost all charcoal in the US is made from oak and hickory (mainly oak), which starts out as slabs cut off logs at the sawmills. Slabs being the outside edge you cut off to take a round log to square for dimension lumber. These long slabs are then bundled and stacked into large sheds (kilns) where they are heated and turned into charcoal.
Taken directly from the kiln and broken down into small pieces and bagged, you have lump, which is 100% charcoal. Rocks and other stuff are part of the process of loading and handling this stuff with highloaders. A lot of it done on gravel lots vs. concrete floors.
Briquettes are made from the same lump charcoal, but ground to a fine dust, then mixed with sand, sawdust and other binders in a wet slurry, then pressed into shape. They are not 100% charcoal, but have those fillers and binders. Convenient and consistent, but not the quality of lump. Less heat and more ash and residue when you are done.
Each kiln and charcoal maker may make and bag for dozens of labels, so brand isn't all that important. For dutch ovens, briqs are the way to go due to their consistent size and burn rate.
Over the long haul, I've always found Royal Oak to have less fillers than say Kingsford and most store brands made to the Kingsford mix. So the RO burned hotter and longer.
COWBOY, so I hear, is made from drops from a hardwood flooring manufacturer. In theory, this would be ideal and it would be mostly heartwood vs. sapwood and bark from traditional makers. Of the two bags I've tried, it had some other stuff in it, including what looked to me like partially kilned pine. It would be last on my list of charcoal to buy.
