To be honest, until Adobe changes Flash, I think Java is the best bet in terms of responsiveness (there's still random garbage collection delays of around 100ms so not perfect; but an improvement). Installation base is comparable to Flash.
But not in terms of design: for although a Java version theoretically could be as pretty as your Flash version (and it is very pretty), the designer-tool support really isn't there. It would be hard to port; and hard to modify. Sun has some tool support for designers, but I'm sure it has nightmare usability.
I think both design and responsiveness are crucial in your space, so this is a difficult one.