Hi there, if you already choose jBPM I think that jBPM5 is the way to go. As far as I know the jBPM5 code base has the same maturity as Activiti.. jBPM5 was the result of couple refactorings and rebrandings from project called Drools Flow. The main advantage of choosing jBPM5 is of course the use of the BPMN2.0 standard and the great integration with the Rule engine.
Depends on your situation, but if you really want to do cool stuff a Rule Engine and the Complex Event Processing features can be very beneficial to your projects!
Greetings!