Underlays

Regarding underlayment for laminate floor... If you've installed one, did you use the basic or sound deadening We're going to install 700 sq ft of shaw laminate wood floor in the livingroom/foyer/diningroom and hallway. This is a triplewide manufactured home - it has a moisture barrier under the house (one that covers the underside of home, and one that covers the dirt under the house.) The house sits up on piers with cinderblock facing. It's got 3/4" plywood under the old carpet. Moisture isn't a problem. The house does have vaulted ceilings. (which increases echo). I'm trying to decide between using the basic foam underlayment or going with a sound deadening one. A local home center said they've only installed the deadening type in 2 or 3 homes in the last 4 years. Virtually everyone goes with the basic (since it's free). We will have a large area rug in the living room. If you've put in a floating floor, which foam did you use and how were the results? If you used the deadening, do you think it was worth the extra money?