It is both challenging as well as interesting to observe the conflict of choices as technology move too fast in their respective fronts. My preference will be if a particular alternative already has a powerful gravity of content and community behind it, most likely spurred by some starting but comprehensive tutorial-friendly content, for example http://code.google.com/webtoolkit/artic ... cture.html
demonstrates a good reference for newbies to pick up on.
About GWT in iDempiere, Heng Sin is right that it is far from production as right now i am putting up the code for WorkFlow panels which are missing (together with Process menus). I find it very engaging and interesting to master new stuff and i welcome anyone to join in. All progress i have uploaded to my repo.
If you are interested to work on exactly my area of concern i.e. GWT, i be happy to give a session of explanation on its progress and gaps at our next irc session or if you prefer a skype session.