Some recent personal experience on the
matter. I've been using Sun's Forte CE
for quite a while, and today it
suddenly broke. Not sure why, but
rather than try to fix it, I thought
I'd try some newer alternatives.

JDeveloper worked after downloading
the full install. (I tinkered with the
base install for a while before giving
up!) It worked, but it ran slower
than -- as they say -- molasses in
January, and I couldn't get it to
build JAR files in any way that made
sense. It kept wanting to clutter
them up with its own directory structure.

Then I found that Borland has a personal
edition of JBuilder for free. That
went a lot smoother after I figured out
that the help docs were a separate
download. You don't get a lot of stuff
with the personal edition (JavaDoc,
EJB, CORBA, can't remember what all)
but you can do applets and beans, and
since applets are pretty much all I'm
working on right now (and some JSP
another way) it seems like it'll work
for me.

Based on all this, and assuming Sun One
is a lot like Forte was, my vote goes
to JBuilder, too.