C farmer: I'm no expert, but I've heard that lump charcoal burns hotter and faster, so it might not be good if you're trying to keep low temps for a long time. I've aslo heard that Kingsford tends to burn more uniformly (especially better when using the Minion method).
But, be forewarned: I pass a Home Depot on my way home from work, so I stopped there today, and bought the two-pack for $12.88. Didn't notice the huge tear on one side that was covered very poorly with packing tape until I got home and found a mess in my trunk!
Figures. A whole pallet full of charcoal, and I happened to pick up the damaged one! I've had that sort of thing happen before, so I should have known better.