Trying to accumulate airline points on either Delta or Northwest but don't fly that often and usually only a short distance when I do. I was wondering which Visa or Mastercard is best to have if you want to rack up airline miles without flying much. I stay in a lot of hotels but most of my travel is by car so my business expenses are mostly gas and hotel rooms. Knowing that, which Visa or Mastercard is going to be best for getting air miles on Delta or Northwest Airlines and Why.

Also I have always thought it was better to have a low say (say 8.9%) VS. having an affinity card so like to read some schools of thought on that as well.