AcJet no longer exists. That certificate was closed and all of the DL Connection flying was merged onto the ACA certificate. It has been a while since I interviewed but they have always placed people in airplanes based upon the need at the time. You could go into either the DL or UA side. I can't really tell you what times are competitive right now as that's all changed since 9/11. The current bases are:
IAD (UAX)- CRJ, J41, 328JET (as of 3/02)
ORD (UAX)- CRJ
LGA (DLConn)- 328JET
BOS (DLConn)- 328JET
All J-32's were retired this past Monday (12/3).
Hope this helps.