Best way to perform currency conversions

Hi experts,

I got a researching task to find out where to best perform currency conversions in SD-reporting in SAP BW 7.3:

We have three options:

1. Currency conversion in the query during runtime

2. Currency conversion in the query via formula

3. Currency conversion in the data flow

a) in direction to InfoCube

b) in direction to DSO

Which one is the best regarding feasibility, flexibility, sustainability, performance etc. ?

Thank you very much for your help!