Hi Nikhil,
SAP FICO module deals with Finance(FI) and Controlling(CO) modules of SAP ERP system. They areintegrated with Sales and Distribution Module ( SD) and Materials management (MM) module. SAP BI/BW are SAP Add-On Module.
In SAP, we have two roads to travel : Technical and Functional module. Think before you proceed. If you are willing to go to SAP FICO. Explore more in SAP FICO and then you can proceed. If you think if you can sail in SAP boat, definitely you can sail till the end of your career. SAP BI module involves importing data from different repositories/databases and If you are interested in that, you can proceed with that. Each and every module in SAP is having different flavour and taste.
Reference:
Actually, I am from SAP PI module and I have some idea about other modules too. Currently I heared from many consultants SAP BI is hot. You can proceed with that. If you are willing to go to SAP FICO do some more research then proceed.
All the best!
Regards
Hari Suseelan