experience and quals will help you get hired and then will have absolutely nothing to do with what you get as a new hire.
there will be say 20 people in class and 20 assignments available. the latest rumor I heard is that seniority within your class is determined by age. (oldest guy is most senior). I am not 100% that is how they are doing it, but whatever the method is, the most senior pilot in the class gets his/her choice of the 20 assignments. It goes down the list to the next in line and he/she has 19 to chose from, and so on, until the last pilot (the 8 ball) gets whatever is left.
As it stands right now, there is no 737 base in DC, so if you want to be based there, you would want to be on the A320 or the 57/67. Doesn't mean they won't open a 37 base there, I just think it is going to take awhile before they do that.
If you get a 320 I don't think it will be hard to get back to DC. They went "unfilled" there last spring, so you may even be able to get it straight out of new hire.
We are supposed to get info on the new bidding process sometime this week and they are expecting the first of the new bids for the combined list to close in early October. Once the results are posted from that, we will have a much better idea of what will likely be available for new hires later this year.