My silver dollars are like chipmunks, they will constantly pack food into their mouths and then juggle the pellets until they can eat them all. And if one has food and the others don't they will chase it around until it drops it and another picks it up - this continues ad nauseum.
i havent kept many kind of fishes yet, but i would say my Red Forest Jewels. They are very opportunistic and eat way beyond their limit. Rounded belly and lying on the floor too full to swim..