Jenkins Build Flow versus Workflow (Pipeline) plugin
Pipeline / Workflow is based off concepts from the Build Flow plugin. Based on the wiki notes here: https://wiki.jenkins-ci.org/display/JENKINS/Build+Flow+Plugin it would seem like Pipeline is the future of Build Flow. I know for a fact that Pipeline is considered a a core strategic initiative for Jenkins 2.0 by Cloudbees and will be a front and center initiative going forward.
https://wiki.jenkins-ci.org/display/JENKINS/Jenkins+2.0
In short, I would move to Pipeline to be ahead of the curve.
Build Flow is the predecessor of Pipeline.Pipeline is more complex and more powerful (flexibility, features, integrations, etc).