While sponges are most commonly thought of as mechanical filtration, they also provide significant surface area for growth of beneficial bacteria. There's a good discussion about media in the equipment section right now. One source linked there claims that 20-30ppi sponge is superior to most dedicated bio-media in terms of biological filtration capacity. They have a bunch of data on surface area, etc but don't really say how they came up with all of it. So I guess take it with a grain of salt.
If you have a low to moderate fish stocking, and an appropriately sized filter the optimizing of media may not give much if any improvement over what comes with the filter. The tank is only producing enough waste to feed a certain amount of BB. If you have enough surface area for BB to colonize and process 100% of the waste, doubling that surface area won't really do anything. Now if the BB are maxed out and can't keep up with the waste, that's where optimizing could help. Overstocked tank, undersized filter, etc.
There are other things you may want to consider like cost, maintenance interval, effect on flow. For example changing media might reduce flow through the filter. Going to multiple fine floss pads might plug up quickly and need to be cleaned and/or changed frequently to prevent loss of flow. You could spend more money for a "high end" bio media (Biohome, Seachem Matrix) that may or may not give any benefit.