Credit Card Programs - Which BoA Credit Card?

My fiance and I are consolidating our accounts (moving from my Wells Fargo to her BoA). We are looking to open a joint CC and not sure which one, we'd like to earn airline miles more than anything else. I typically fly NW for work, she usually flys Delta or Airtran for her personal trips.

Any recommendations?

Why does it have to be BofA? I don't think there are any real benefits to having your credit card accounts be in the same bank as your checking account (except for high-asset programs such as Citigold which give annual fee waivers). If your primary airlines are NW and DL, the Amex SPG card would make a lot of sense.