Hi Lavanya,
Whether it is a single stack or dual stack system, it is always better to use Proxy, until and unless there is a business demand to use RFC.
Proxy
--> Proxy communication is better than RFC/BAPI communication when performance is concerned.
--> ABAP Proxies uses Web service and HTTP Protocols.
--> Proxies is used for both Sync and Async. If you use ABAP Proxy , you can reduce the overhead calling the function again and again..
--> Proxies communicate with the XI server by means of native SOAP calls over HTTP .
--> Proxy is used for large volumes of data.
--> proxy it is used to process the Mapping and rooting on Integration Engine bypass the Adapter.
--> In proxy XI communicates with the R/3 in native XI language (SOAP XML).
RFC
--> RFC/BAPI has its own overhead of function call.
--> RFC, the data is converted between RFC and XML in RFC adapter.
--> So you have to convert from SOAP to RFC calls and vice versa. So XML conversion is required.
--> RFC is more riscy becoz of less stability and bad performance.
--> You have an additional application (Java Adapter Engine) running during message exchange.
Regards
Bhargava krishna