Hi Gaurav
This is a case specific question and since you have not mentioned much details its difficult to comment Also note there are no pros and cons .. they are 2 different options which should be looked at in discussion with the client as well as taking into consideration the existing system landscape
Check the below link and it explains all scenarios mentioned above as well as a mixed scenario as well ..
https://websmp207.sap-ag.de/~sapidb/012002523100011490632014E
However the inital decision should be based on answering the following questions
1. Which system is upto date for installation of SLM
2. incase of SRM the netweaver portal seamlessly integrates to SLM
3. What are the specific tasks which needs to be taken care of like ..
If SAP Supplier Lifecycle Management is deployed on SAP SRM configured as a SUS instance, the integration with SUS is also supported.
For SAP Supplier Relationship Management back-end systems connected to SAP Supplier Lifecycle
Management 2.0, the following component is mandatory
Integration Component for SAP Supplier Lifecycle Management SRM Back-End System 1.0 SP08
SMCSRMIT 100 SP08
For SAP ERP back-end systems connected to SAP Supplier Lifecycle Management 2.0, the following
component is mandatory
Integration Component for SAP Supplier Lifecycle Management ERP Back-End System 1.0 SP08
SMCERPIT 100 SP08
let me know if that helps !!
Regards
Vinita