I used my UDS last year, and my old used Brinkmann SnP offset the year before. Directly on the grates. Milder wood. Pecan, apple, any citrus tree, mulberry, mix in cherry; personally I'd avoid mesquite and walnut. Or very small amount of the latter with any of the former mixed in. The more I use it, the more I like the medium large bags of hickory hunks available fairly readily, ie KMart, Wally World, several hardware stores. Those fist sized chunks are just too convenient. And I even split a few, to double the surface area. Good luck.