Kimmel's is all I have ever used -- it's all that's available here without driving 40 miles (not happening -- I like to overload to save trips!
I've never had a problem with the way it burns (nut coal), but in the past, I have had several pounds of trash out of 3.5 tons: Once had a grapefruit-sized boulder in the bag, I've had smaller rocks jam my grates open requiring more than one cleanout, I've had sticks, roots & what looked like pieces of railroad tie (don't care much about those -- their light & they burn) & once had a ball of dried mud bigger than a grapefruit with a few rocks inside & weighing about 10 lbs, in one bag. I've also found strands of electrical wiring ( those burn/melt ). This was all in one season! When I picked up that load it was loose bags. I didn't have a bigger trailer at the time & a 2500# skid would have blown out the tires as soon as the forklift set half the weight down! I think the kids working there were handing me stuff out of the rejected/returns pile. Now I just buy sealed pallets & count the bags as I stack them in the basement.
Last season, I had not one piece of anything out of 4 tons.