Hi there, you can use both. They have very similar features. This is just a transition state, jBPM5 will probably released at the end of this month by krisv.
I recommend you to start with jBPM5 for the following reasons:
1) jBPM5 is drools flow code base
2) You can help us to test it and report issues that we can quickly fix for you
3) the transition between drools flow and jBPM5 is almost done
4) jBPM5 is stable as drools flow was.
Greetings!