The first 3 in your list are most popular.
However, I think mastering JDK means a mature Java developer. Some poeple cannot configure IDE. Some poeple connot code without IDE. Not good.
Is Visual Age3.0 OK? I got a Visual Age3.0 Enterprise Version. To my surprised, it supported only JDK1.0.7. How can I update it to 3.02 or 3.5 or just update JDK to JDK1.2?