Garlic powder textures like cornstarch. Granulated garlic textures like salt, but doesn’t melt or dissolve. The finer the granulation, the better. Shop around.
Most markets now carry only the granulated, yet label it as garlic powder. Ninety-nine percent of the time I use granulated labeled as powder. I know it’s confusing, but that’s what manufacturers do.
If you shop at a specialty market or wholesale food store, you’ll be able to buy granulated labeled as granulated, and powdered labeled as powder.
If you want extra smooth, then use powder. If it doesn’t matter, then use granulated labeled as powder, or labeled as granulated. The powder is white and the granulated is tan.
* The same is true for onion powder vs granulated onion.