This is different for everyone. It really is depending on what your diet is. Some foods do not break down and have a heavier texture than others when expelled.. Some will float in the toilet while others will sink. Not see as a gross question.
Conventional medical wisdom attributes Floaters to the amount of fat in your poop. While this IS true for certain diseases (cystic fibrosis, celiac disease, biliary atresia, abetalipoprotenimia and a few other weird sounding illnesses), it is NOT true for your run-of-the-mill healthy person!!!
Vegetarians would have you believe that the "perfect" stool (that is, one uncontaminated by the consumption of animal parts) is the Floater. Many vegetarians have spent their entire lives in the quest to produce perfection -- when in fact no particular diet can reliably produce Floaters. The vast majority of us bring forth Sinkers.
Actually, it is gas that does it. Increased levels of air and gas in the poop make it less dense, and cause it to float. Simple as that. Dietary changes can lead to an increase in the amount of gas produced by the bacteria that live in the gut, which is probably what the vegetarians are basing their whole "perfect stool" theory on. I don't know
So I am forced to assume that Floaters are NOT the most desirable of all stools. Sinkers are by far more common. Don't spend your life chowing down on tofu burgers just because you think you are being cheated out of a Floater. Neither tofu burgers nor Floaters are worth the trouble. Sinkers are our destiny.