You're giving up a lot in terms of seniority to go to Delta, but you already know this. I think living in base is always no-brainer, so it'd be hard for me to not recommend Delta for that reason. However, living 3 or more hours away from DTW isn't what I would consider living in base either. Since - in my opinion - you're commuting in both scenarios (ORD with AA or DTW with DAL), you're better off staying where you're at. You're going to see better schedules a lot sooner with AA, too, with the amount of retirements AA is experiencing. If you move closer to DTW and family, that probably tips the scales in favor of Delta.