I think the benefit is with JavaScript API, just because JavaScript is embedded in HTLM5. For future use especially in moving towards Mobile, HTM5 is the way to go. So you don't have to worry about any plug ins like flash for Flex, silverlight etcs. Correct me if I'm wrong, but I believe Adobe will discontinued support flash when it comes to Mobile, and fully support Flash in HTML5. So it makes sense to go with JavaScript API, I think! Although I think Flex is really "sexy" looking, in term of cosmetically/esthetically, I really haven't seen JavaScript being that good looking. But then again I haven't really use JavaScript with Ajax yet, so I could be wrong. What do you guys think?