I started learning JavaFx just after it released, as JavaFx is based on java it has the power and maturity of java by born. I wanted to use JavaFx as an alternative to Flash. Though i was learning Flex framework and actionscript3 before starting JavaFx, and i was not so serious about that RIA thing then, and i can’t afford much time for Flex then. But after JavaFx released i was so excited and i started learning and doing javafx seriously. I was very excited about its power and possibilities. From a developer view Javafx runs on a JVM which is more then 25 times faster then Tamarin VM (used in flashplayer), you can deploy javafx project virtually on any platform, and any device (though flash now have support for desktop and mobile devices).
But from the user view javafx is just a slow dumb shit (at least for now). User don’t like to download a more then 15MB jvm and install while visiting a websites on the other hand flash player is only less then 2MB. If you already have the latest JVM installed then to view a javafx project for the first time, it takes little long time because it has to download few more jars from javafx’s server to serve javafx which costs some time and a bad user experience (yes Sun aware of this problem and they are working on it). Flash has none of this problems. So for now it seems Flash is the right choice
I think learning both Javafx and Actionscript both are better for any developer. If you know more you will have more choices.
see JavaFx performance here.
see ActionScript3 performance here.