The dumpster theory.
Many posters agree with this theory
A proper grave would take quite a bit of digging, would require some time(risk of being seen), and Casey seems too lazy to do it.
The "feed her to the alligators" theory (ugh) is popular, but to make sure the body was not seen from the road, Casey would have to carry it a short distance into the swamps
I don't know about you, but walking into an alligator filled swamp or lake at night scares the hell out me.
Throw her off a bridge? maybe, but bridges are very exposed, too much risk of being seen. Someone might report her just because they think she's dumping garbage.
A Dumpster is quick, convient, and nobody would think twice if she were seen.
Don't know what its like in Florida, but where I live, we put out our garbage at night(I put mine out at 1-2 am).
Once the dumpster is emptied at the dump, finding Caylee would be almost impossible.