My spotted lays on the bottom all day, then comes to top at night. my alligator never lay's on the bottom, he's either floating on the top, or hes hanging vertically in the java ferns. He's a young of the year, so he's pretty small still.
mine generally is at the bottom at night unless he's coming up for air, mine swims around a lot actually but i don't think that there is anything wrong with that.