I prefer the sponge because you can clean it, as where gravel has to vacuumed, which is a little tight for a two gallon. Also sponge is tranferable to another tank if so needed as where UGF is stouck in tank. Also, if you use a sponge, make sure to clean it in room temp, declorinated water to preserve bacterial colony in sponge. *twirlysmiley*