Charcoal is made by burning wood in the absence of oxygen, and lump charcoal is the product of that. Since lump is charcoal in its most natural form, it's no wonder purists will almost always prefer it. Beyond that, lump charcoal has a lot of attractive qualities; it lights faster, burns hotter, and leaves very little ash compared to briquettes. Lump charcoal is also more responsive to oxygen, making it easier to control the fire's temperature if your grill has adjustable air vents.
Briquettes are kind of like the fast food of charcoal; they're cheap, reliable, can be found on almost every corner, but you really don't want to know what's in them.Unlike the pure lump charcoal, briquettes are manufactured wood by-products compressed with additives that help them light and burn consistently. These additives do give off a chemical smell when lit, but allowing them to burn until covered with white ash before starting to cook should avoid any off-putting smells transferring to your food.