Question

Which one should I use?

Is there any reason to use one rather than the other?

Is one better for error handling?

$.ajax({
    url: url,
    data: { start: start, end: end }
}).done(function(data, textStatus, jqXHR) {
    $('#myElement').append(data);
}).fail(function() {
    // report error    
});

OR

$.ajax({
    url: url,
    data: { start: start, end: end },
    success: function(data, textStatus, jqXHR) {
        $('#myElement').append(data);
    },
    error: function(jqXHR, textStatus, errorThrown) {
        // report error
    }
});

Answer 1

The two options are equivalent.

However, the promise-style interface (.fail() and .done()) allow you to separate the code creating the request from the code handling the response.

You can write a function that sends an AJAX request and returns the jqXHR object, and then call that function elsewhere and add a handler.

When combined with the .pipe() function, the promise-style interface can also help reduce nesting when making multiple AJAX calls:

$.ajax(...)
    .pipe(function() { 
        return $.ajax(...);
    })
    .pipe(function() { 
        return $.ajax(...);
    })
    .pipe(function() { 
        return $.ajax(...);
    });