Using $('#myDiv').click(function(){ is better as it follows standard event registration model. (jQuery internally uses addEventListener and attachEvent).

Basically registering an event in modern way is the unobtrusive way of handling events. Also to register more than one event listener for the target you can call addEventListener() for the same target.

var myEl = document.getElementById('myelement');

myEl.addEventListener('click', function() {
    alert('Hello world');
}, false);

myEl.addEventListener('click', function() {
    alert('Hello world again!!!');
}, false);

http://jsfiddle.net/aj55x/1/

Why use addEventListener? (From MDN)

addEventListener is the way to register an event listener as specified in W3C DOM. Its benefits are as follows:

• It allows adding more than a single handler for an event. This is particularly useful for DHTML libraries or Mozilla extensions that need to work well even if other libraries/extensions are used.
• It gives you finer-grained control of the phase when the listener gets activated (capturing vs. bubbling)
• It works on any DOM element, not just HTML elements.

More about Modern event registration -> http://www.quirksmode.org/js/events_advanced.html

Other methods such as setting the HTML attributes, example:

<button onclick="alert('Hello world!')">

Or DOM element properties, example:

myEl.onclick = function(event){alert('Hello world');}; 

are old and they can be over written easily.

HTML attribute should be avoided as It makes the markup bigger and less readable. Concerns of content/structure and behavior are not well-separated, making a bug harder to find.

The problem with the DOM element properties method is that only one event handler can be bound to an element per event.

More about Traditional event handling -> http://www.quirksmode.org/js/events_tradmod.html

MDN Reference: https://developer.mozilla.org/en-US/docs/DOM/event