The best buds are popcorn nugs. When you grow huge buds, especially the main cola, with a near perfect grow, you'll find as you break up the cola to remove stems for jarring, that they are exactly that, popcorn sized rock hard little nugs. You won't get them like that with a pure sativa but the more indica in the plant the tighter they will be. Sativas tend to be more airy to help deal with the hotter climates.
The ones down low on the plant are more airy and fluffy. Mostly because of less light and just the way the plant has evolved.