Ajax file uploading vs Form uploading

I have created a site where users can upload an avatar. I want to make the avatar upload very easy and seamless, this leads me on to my question: should I use ajax uploads or form uploads to update a users profile picture? If I am expecting large amounts of traffic which one would be better ? Also, usability wise?

I have come to the conclusion that AJAX would be better for usability and creating a fluent transaction, but many people say to stick by traditional from uploading when it comes to images?