ECC on HANA Vs BW on HANA

Hi All,

We have the ECC and BW  system in our landscape and We are still undecided on how to go on HANA, wether to go with BW On HANA first and then with ECC on HANA or first to go with ECCon HANA then shut down BW after some time.

Our Business core requirement is "Real time reporting".

I want to PROS and CONS of going with HANA in ECC and as well as on BW.

Please share your inputs.