I use regular K -
However, I went through about 250 pounds of Cowboy charcoal last year in my CG Outlaw. The only reason I switched is because the wife always complained about the smell of Cowboy charcoal.
I've tried lump in my UDS but, when you can get 40 pounds of regular K on sale for under $10.00, what's the use? Regular K does great mixed with a little hickory. But, use what you have. All of it works well in a UDS.