Not sure what extra perks you would get from having status on AA if you already pay for all F/J tickets. You could say lounge access, but you can get that with only a $450 Citibank AA credit card. If it was me, I would stick with DL (provided they have non stop flight times that work for you in your home city). You may not get extra status on AA, but DL's product (on-time performance, IT, staff training) is the best in the US airline industry. Either way, it is not going to have much affect on your air travel experience.