Personally I prefer using the JSON API rather than the others (Rest, Soap). JSON is working perfectly well with Javascript, and I can easily integrate with some cool Ajax interfaces.

Here is a image app I built. It simply pass a request to the Flickr API, and get the most recent uploaded photos, then return the data as JSON. Finally I just use Jquery to make some fade in, fade out effects.

Feel free to view the page source to find out how it works. It’s a pretty useful skill, and you can start building your own APIs once you get used to it. With the same techniques, I built the image widget for LEWIS imagebank.