I run a fairly deep sand bed in both of my 120G tanks, one of them being around 6" at it's deepest point, and another being around 4", I prefer the aesthetic look of a sand bed over bare-bottom, but If I were to do it again, I'd probably go with a SSB or go bare-bottom. If you're after critters like gobies that live in the sand and caves around live rock, you may opt for a DSB. There's a lot of anecdotal eveidence supporting both sides of the issue. Like most things in this hobby, it comes down to husbandry in the end.

Eric