DFW = very senior. To put it in perspective - I am in my 14th year and can just now be a bottom lineholder/senior reserve MD80 F/O. I can also just barely hold 737 F/O, but deep reserve.
That said - when AA is in hiring mode, as it was in '98-'00, you could bid and get awarded DFW within a month or two of new hire class. Heck, in early '00, some of my classmates were awarded DFW 75/76 Int'l F/O within a couple months. So when we start hiring again, you should be able to get a DFW slot relatively quickly. But you will be on reserve a LOOONG time.
In shrinkage mode, DFW is the first to start displacing out of base. During the past ten dark years, there were guys bumped out of there that weren't reinstated for a good 7 years.
MIA = *THE MOST* Junior base we have. Even more junior than NY. Thatis where the majority start as new hires, and guys used to joke that in furlough mode you will do the "Miami Death March" where you slowly bump down to the most junior equipment out of MIA before you get canned.
I am currently based in MIA and it has pretty much the best flying in the system. Europe, Deep South, Caribbean and Domestic. All that's missing is Asia, hopefully that will come when we get more 773s on line. As a 14th year 75/76 F/O I am about 65% on the list in MIA, flying only Caribbean and S America Lite stuff (no all nighters.) Sweet bid status. MIA is slated to grow the most out of all our bases. It is a cash cow for AA and a great base to fly out of.