Hi Shree,
SAP BI or HANA is good option. both are having there own advantages. As u know have .NET experience you can be a good developer in HANA. Also ABAP is not much diffult and as you can understand functional and Warehouse aspects then BI is also not bad.
It is not totally based you what you want if you want to work on Dataware house and reporting kind of tool then BI is good. Of you like to learn more on Businss Process and its customization perspecting HANA is good option. I can't see still customers are moving to HANA so fast but in future they need to.
Also one thing in HANA you have many other aspects like administration where you can also look for.
Check documents on help.sap.com to get what these modules do and then decide on your interest area.
Regards,
Ganesh
