"javascript:void(0);" vs "return false" vs "preventDefault()"

When I want some link to not do anything but only respond to javascript actions what's the best way to avoid the link scrolling to the top edge of the page ?
I know several ways of doing it, they all seem to work fine :

<a href="javascript:void(0)">Hello</a>

or

<a id="hello" href="#">Hello</a>
<script type="text/javascript>
  $(document).ready(function() {
    $("#toto").click(function(){
      //...
      return false;
    });
  });
</script>

and even :

<a id="hello" href="#">Hello</a>
<script type="text/javascript>
  $(document).ready(function() {
    $("#toto").click(function(event){
      event.preventDefault();          
      //...
    });
  });
</script>

Do you have any preference ? why ? in which conditions ?

PS: of course the above examples assume you're using jquery but there's equivalents for mootools or prototype.