Over the years I've used many brands of lump including RO, B&B, Stubbs, Cowboy, several brands of mesquite, etc.,etc. and the only one that I was REALLY impressed by was "Wicked Good". The smallest pieces in the bag were about golf ball size while the biggest was similar to a split log while the majority of it was about tennis ball size. It burned really hot and left very little ash but the biggest difference that I noticed besides the size of the pieces was the density of the stuff and the length of the burn that it gave me. It actually reminded me of porcelain tile because of its hardness and weight and I was able to reuse some of it in my next cook whereas other brands would have all incinerated to dust! It's a little pricey but I think that "Wicked Good" is one of the real standouts in the world of lump charcoals.
Never Trust A Skinny Cook!!!
Lone Star Grillz Vertical Offset, New Braunfels Black Diamond Offset (Retired), Weber Kettle