Oak Cubes

Arguably better than chips, oak cubes are toasted with a gradient that penetrates slowly into the wood that better replicates the effect of a charred barrel. French is softer and more gentle, American is more robust and intense.  Lighter roasts give more "woody" character, heavier char gives you more smoky roasty flavors and aromas.  

Lighter wines and beers should typically use lighter roasts and more French, heavier more robust wines and beers can stand up to American Heavy chars.