Originally Posted by Blackhawk

People on both sides will give you their version of the truth. Frankly, within the time frame of you being a FO there is a good possibility that the two will be combined. If that happens, date of hire will have a big impact though it probably won't be the only consideration so if you can get an earlier class date with one versus the other that should be a major factor.
Pilots tend to chase upgrade times, but that tends to make upgrades like hot stocks. If you get in early you make a killing. Those getting in later, not so much. They may get hired when upgrade times are at 1 year, but may wait 5 years or more due to the "wave" of pilots chasing the upgrade.
The inverse applies. ExpressJet "stock" has been knocked down. New hire classes since the Delta announcement have generally been small. Many of the FO's left- look at the comments by former XJT pilots now at CommutAir. Many high seniority captains left, either for places like K4 (about 130 senior pilots were hired by them), other airlines or sectors of the aviation industry such as 135 and corporate, or just retired to avoid commuting. This means that when upgrades do start again you will see the upgrade times plummet. They won't be "linear".
I've seen this before and more than once. When I was hired at ASA I was told 5-8 years to upgrade. I had friends who went to ContExp for the quick upgrade, then running about 2 years if I remember right. Delta bought ASA while I was in new hire class and 18 months later I was upgrading. Could have been faster if I went to the EMB-120. Those friends who went to ContExp for the quick upgrade came over to ASA 5 years later. They were still FO's with no end in sight at ContExp.