Hi Bhargava,
I believe this is not the best forum for those questions.
Please consider the HCP space or the PI space:
Process Integration (PI) & SOA Middleware
That being said, if you have very SAP-centric (IDOCs, RFCs, ABAP Proxies), you'd probably better stick with PO. HCI can consume IDOCs and RFCs if exposed as SOAP Web Services, but that'd be overhead if you already have the integrations done.
HCI is more oriented to newer and simpler integration paradigms, supporting SFTP, OData/Rest (HTTP) and SOAP mainly. It also supports IDocs through IDoc Soap connectivity. Check the latest roadmap:
https://service.sap.com/~sapidb/011000358700000367352014E.pdf
But more than protocols, leveraging either HCI or PI is more a decision based on location. Imagine you want to integrate 2 applications in your intranet - no point for HCI right? But if you're trying to integrate an intranet application (say, ERP) with different endpoints distributed all around the globe, internet connectivity starts to be an issue, and hence HCI might be a better option.
Best regards,
Henrique.