It very much depends on what you need and which restrictions apply to your technology choice. Could be that there are certain technologies disapproved in your company or at your customers or you just can't get development resources for it.
Most naturally you would either go with the .NET or Java camp. Java - IMHO, of course - has the big advantage that you can get an open source library for almost everything whereas Microsoft wants to have your bucks pretty soon. Plus you don't have any resctrictions as to which platform ( Windoze vs. *nix ) your server backend should run.
Very accurate and strong in all respects is not very clear to me - sound like "everything". If your web pages need to be rich in functionality ( still depending on the richness you really need, like providing the usability of classic GUIs ) you will most likely end up with a RIA framework of sorts sooner or later. If your web page needs to just stun the visitor with its cool design than HTML5 is the way to go. Still these two do not exclude each other as any RIA framework most likely will be based on Java Script and Ajax for the richness where the Java Script objects will live inside an HTML page in the browser.
We use GWT ( Google Web Toolkit ) for some reasons. But, from my point of view, what I really like is the straightforward integration of the OpenEdge AppServer in the Java world with the Java Open Client - that really rocks. The same integration does exist for the .NET world too, but I have very limited experience with it and therefore are not able to reommend it.
Heavy Regards, RealHeavyDude.