I want to develop Java apps, real quick, what IDE should I choose?
Do you mean desktop GUI apps? Then NetBeans' GUI builder is alledgedly very good.
For any other class of app, IntelliJ IDEA wins by many miles. Note: it costs money.
That depends on which type of developer you are. You the "emacs" (powerful tool) or the "vi" (get things done) type? I, for example, won't touch IntelliJ IDEA even if I was paid for it (and I am). It just gets in my way. I'm an Eclipse guy. Other people can't stand anything besides NetBeans.
I suggest to download IntelliJ, Eclipse and NetBeans and give each a go. Take one day with each, write a piece of code and see how it fits you. Do you get around? Or does the IDE get in the way? Can you quickly find what you seek or are you drowned in options? Does the ride feel smooth or bumpy? Do the defaults match your personal preferences?