I find that Pivotal is pretty opinionated with the workflow you use. Specifically, it is meant for an agile process that is exactly that Pivotal (the consulting group) uses to develop their client products.
Pivotal is extremely opinionated. Seems like people love it or hate it. JIRA is totally unopinionated and is what you make of it. I've had awful JIRA workflows imposed on me and it's the worst. My current company is generous with admin rights so we pick the flow we want for every project and it's great.