My advice is for you to goto Comair. I have a few friends at Pinnacle and they say the company is very unorganized. In addition, the FO pay at Pinnacle is terrible. $20 first year, $24 second year...sorry but for me, I would not work for those wages. Comair pays $23 first year, and $37 or $41 2nd year depending on if you're on the 50 or 70 seater.
Another thing you'd want to consider is where you want to live. If you live near one of the Pinnacle bases, you might consider going to Pinnacle. If you goto Comair, get based in JFK, and move to NY, that $37/hr. 2nd year doesn't take you very far in NY, let's not even talk about what $23/hr in NY will get you. So those are other things you need to think about. If you don't live in one of Comair's or Pinnacle's domiciles and have to commute regardless, then my pick is definitly Comair.
Don't try to outwit the system, you'll lose. If you try to figure out where a company will be in 5 years or how upgrade will be in 5 years, no one will know. If you know that info, you're in the wrong business, you need to go be an stock picker for Merryl Lynch. Who knows what will happen to Comair if they are sold or if Delta goes into bankruptcy. Because if Delta goes to bankruptcy, Comair goes also, which means concessions most likely. Again, don't try to figure this out. I don't even know what will happen in 5 days, let alone 5 years.
Enough advice from me, good luck with your decision. Remember, any decision, even if it's the wrong one, is better than no decision. Make your choice, stick with it, and make the best of it. Hope this helps.
-W