Note that OpenCensus is the only actual standard for what has to be defined to really have distributed tracing. OpenTracing leaves almost everything up to the implementation, which does not produce compatible libraries. OpenCensus provides complete specs and implementations for distributed tracing across multiple systems. This also involves some W3C standards, Trace Context and https://w3c.github.io/correlation-context/
OpenCensus and OpenTracing will ultimately be merged and the result live under CNCF. So choosing OpenCensus is a safe bet.
Also note that we who work on OpenCensus have been discussing with those who work on Spandex to combine efforts.
I hope the OpenCensus library can become the “telemetry library” of distributed tracing on beam 
– we’ll also be integrating with telemetry for statistic reporting.
