setTimeOut() or setInterval() . 4 methods to apply same thing. which is best?

I am displaying a countdown watch with respect to a given endtime.

although its working perfect but i want to know which is best methods to apply.

below is my countdown function.

  var timerId;
  var postData = {endDate : endDate, tz : tz};  
  var countdown = function()
    { 
      $.ajax({
               type : 'post',
               async : false,
               timeout : 1000,
               url : './ajax_countdown.php',
               data : $.param(postData),
               dataType : 'json',
               success : function (resp){
                  $('#currentTime').html(resp.remainingTime);
               }
            }); 
     }

what i want is that function (countdown) shoud be called automatically after every 1 second and if it does not execute/completed within 1 second then cancel the current ajax and start a new ajax call.

now I found there are 4 working methods

method 1: using setInterval() with window object

window.setInterval(countdown, 1000);

method 2 : using setInterval() independently

setInterval(function() {countdown()}, 1000);

method 3 : using setTimeOut inside the function an call other function to intialize main function

var countdown = function() { 
     $.ajax({ //ajax code });
     timerId = setTimeout(countdown, 5000); // assign to a variable
 }

function clockStart() {  
        if (timerId) return
        countdown();
}
clockStart(); // calling this function 

method 4 : using anonymous function call

var countdown = function() { 
     $.ajax({ //ajax code });
     timerId = setTimeout(countdown, 5000);
 }
  (function(){
         if (timerId) return;
         countdown();
})();

Please tell me

• What is con and pro of each method and which one is best/right method?
• Should i use clearTimeOut() or clearInterval() ?

References

http://javascript.info/tutorial/settimeout-setinterval

Calling a function every 60 seconds

http://www.electrictoolbox.com/using-settimeout-javascript/