What is the difference between using new Date() and new Date().getTime() when subtracting two timestamps? (test script on jsFiddle)

Both of the following gives the same results:

var prev1 = new Date();

setTimeout(function() {

    var curr1 = new Date();

    var diff1 = curr1 - prev1;

}, 500);



var prev2 = new Date().getTime();

setTimeout(function() {

    var curr2 = new Date().getTime();

    var diff2 = curr2 - prev2;

}, 500);

Is there a reason I should prefer one over another?