- how is the data represented
- is consitency important
- how many writes are happening
- what roles do exist and do i want them in the datawarehouse or the application
- what replications do i need
- can i split the reads from the writes
- what does the least transformations needed to store and load the data
just the from the top of my head. usually i tend to put user as well as financial transaction data in an SQL because consistency is important.
but it's taste :)