If you have one of the service that has expedited TSA screening, then I think walk landside is the best way. Depends on where your DL flight gates and where your AA flight departs but T2-T5 are roughly directly opposite of each other and you can cut through the parking garage relatively easily instead of walking the the loop. If going from T3 to T4, you can just follow the loop. If you DL flight arrives at TBIT or if AA departs from TBIT, I recommend staying air side and do the long airside walk around TBIT north to TBIT south.