Q: Which Apple ID do I use to set up Family Sharing?

I have multiple Apple IDs - one for iCloud and the other I use only for iTunes purchases.  I set up the one for iTunes purchases before I could create a ".me" account, which I use for email, calendar, contacts, etc.  I use the iTunes Apple ID on the other devices of my family members so we can all download the same games and apps.

Now when I want to set up Family Sharing, which Apple ID should I use?  My iTunes Apple ID has my payment information.