This was posted by venetianfrycook in the 'Majors' thread. Your question is answered at the end.

There are currently vacant positions on the E190, B737, and A320. There are open positions in DCA, which tends to run fairly junior. If you get the 190, you'll be PHL-based since that is presently the only domicile on the airplane. However, if you get the 737 or 320, you'll likely be able to bid in to DCA quickly if you don't get it out of the box. (The last class of 2011 was all 320 - except 1 737 - and all of them went to DCA.)

Strictly speculating, I would guess that DCA would be the first 737 base in the east to get axed this coming fall with further retirements as additional A320-family aircraft come on line. (DCA is the smallest of the 3, only about 30 crews there on the 737. CLT is by far the largest, plus the 737 heavy maintenance line is in CLT, so it'll probably be the last to go.)

New hire equipment freeze is 12 months. So, even if you get a piece of equipment other than what you want, you only have to wait a year to get off it. And with the pace of hiring we are projecting, holding the 320 or 737 in any base (as well as the 190, of course) is very likely by the time that freeze is up.