This is a complicated topic. It all depends on exactly what you are trying to do. JBoss provides huge flexibility in classloading configuration, but that does give you plenty of rope to hang yourself with.
Here is are some JBoss classloading articles:
I hesitate to plug our services on a public forum like this, but you could probably use some combination of consulting, training, and support. You really need an analysis of your configuration and applications to get to the best solution. This is a very advanced topic and you aren't likely to get a full answer on the free forums.