Thanks once again for the helpful reply and the links. I'll look at these!
Clicking on the wiki link on OpenIO github page https://github.com/open-io/oio-sds/wiki doesn't give a landing/first page for these links you've mentioned. And I couldn't find these on docs.openio.io.
Regarding best/recommended approach, I was referring to performance/overhead of using various interfaces such as C Library (which I believe will be the fastest barring the network speed between the client and the server), vs. Open IO Native REST API, vs S3 gateway vs. SWIFT etc. Which of these methods offer better performance, security, backward compatibility etc.