I would recommend better start with jbpm 3. jBPM 4 would be too risky for me at the moment.We started a customer project recently with jbpm 3 but made sure, we can switch later on easily to jBPM 5 or Activiti. See http://www.bpm-guide.de/2010/04/17/abstracting-the-process-engine/ for details...
But it is a bit hard to decide exactly now, best is to wait some months ;-)
I must say that I am agree with Bernd. If you need support from red hat, you should choose jbpm3. There is no such support for jbpm4. jBPM5 does not start yet. And Activiti is still in alpha state.
If you choose to use jbpm4, it means that you won't get any official support from red hat. We have only community support, e.g. this forum. So if you have not start yet, please think about it carefully.
And I think jbpm3 is more stable than jbpm4, although jbpm4 is much easier to learn and use. I believe jbpm3 could satisfy all of your need.
Thanks HuiSheng and Bernd, for your suggestion. We will plan to use JBPM3 currently.
I have one more query here, which version of Spring supports JBPM3 as we are using Spring at business layer. Kindly send me some useful link, where I can analyze it.
This should be a good reference point for spring
I am currenlty using spring modules with jBPM 3.2.8 and works great so far.