The latest vacancy saw a lot of movement of bases on the FO side. New hires that are still in training were awarded DFW and ORD (and guys that want LGA will obviously stay there). If you want to be in a specific base, the 145 is currently getting guys to any base before they finish training.
As for time on reserve, this is only an educated guess, but avoid ORD if you want off reserve. Someone on Eagle Lounge ran the numbers on the vacancy and said about 65 FO's are slated to leave ORD and were not replaced. Many of the Captain's flowing to AA out of ORD were not replaced, upgrades were almost all DFW and LGA. ORD is expected to shrink, which is not good for time to hold a line. Time to hold a line will be fastest in LGA, then DFW, followed by ORD.