If you're doing a mix of last minute economy for business, as well as advance purchase economy for personal travel, you should refer to the answer I gave a traveler a few posts up. Until you know how many miles you're going to get from a revenue based program, it's impossible to tell you whether that's better for you than a mileage based program. Sort out what you've spent the last year, and how many miles you've flown, and that should point you in the direction of a revenue based program (Delta, UA) or a mileage based program (AA, Alaska).