Amina,
The development approach will depend on your functionality. If you want to leverage the back end ECC for the RFC and data dictionary structures then development in back end is recommended.
I found that code based implementation is a better approach for my case where I did use most of the data dictionary already defined on my back end to create properties as well for the variable definitions while redefining methods.
Also when you want to use RFC your parameters have to exact , for my case my import and export parameters were different from the outside world call to my services , so it worked better for me to go for code based implementation.
Regards,
AShwini