Their are different subfloors used for different products. What we use for vinyl is a 1/4" exterior grade luan, for ceramic we use a ceramic backer board. In most cases the uneven dips in the floor are caused by crowned joist, which is common in older homes. If you are looking for vinyl flooring, Mannington has a very nice look and durable as well. Mannington has a new look called Nature Form that looks like ceramic tile ( as much as can be expected in a vinyl ), and is warm under foot.