I’m not very familiar with SW FF program but have had status on DL, AA in the past. In order to benefit from any status, the key considerations would probably involve the following:
- area(s) you plan on travel next year and how DL/AA status would be helpful (either directly or via the alliance network). For example, at one point I had status with both UA and AA but a lot of my business/personal travel was to Asia and I found myself flying UA most of the time due to its better alliance network.
- overall airline experience. I found both airlines comparable in terms of customer service but AA seemed to treat me better as an elite whereas DL had generally better planes, entertainment onboard, etc.
- value and planned use of miles. I was able to get good value out of AA miles but not so much from DL miles. DL miles are often referred to as Sky pesos so something to keep in mind if you plan to do a lot of travel & earn a lot of miles next year.
safe travels!