Same here: you plan something and life throws you a curve ball. Personal story: Grad student in MSP (hey MSPeconomist!). I believed I was going to travel a lot with DL last year when I arrived because the gf lives in SBN and the only direct flight was DL. I did a really neat plan of the expenses, how many flights I needed to gain silver, and so on. It all made sense: I had to change from AA to DL.

A month into my doctoral programme we broke up and I never had to fly to SBN.

Two months in, new gf and now I fly with AA to MAD a lot because now she is living there. Never, ever, underestimate the potential that life has to surprise you and to change your plans. I would try to decide, after a few months in, if it is really worth it, and if you are flying a lot. In the mean time, I coincide with the majority opinion, DL or AA.

My only point in favour of DL is that they have a much better programme for –and percentage of– voluntary denied boarding –or bump, in flyertalks lingua is accepting to take a later flight because yours is oversold in exchange for a voucher, gift card or money–, and if you are a student, flying with them and taking bumps every so often, you can make money out of that and use it to buy more flights –thus, eventually reaching status faster.

If you fly enough with DL on a route which tends to be oversold, then I would go for their programme. If not, AA is also a good choice.