Originally Posted by blacknomi
If you say: something puts you at/on the top of the world, it means it makes you really happy.
In the Carpenters song, she feels she physically stands on top of the world looking down on the whole world. You stand on something. No happy connotation here. That's the only difference.
on top/on the top
Both sound OK to me but for the sake of the rhythm I would go with on the top.