Personally I use Web Designer and New BPMN2 modeler. I recommend you to use Web Designer as it supports almost everything that the engine and it is web based integrated with guvnor which allows quick deployment to the running jbpm engine. But if you are more eclipse user then new BPMN2 modeler will do just great.
P.S.
As far as I know boundary events are supported in web designer, What version are you running on?
HTH