I work at Mesaba, but for what it’s worth, I think Mesaba is the way to go. At Mesaba, I’ve seen a large number of people coming from Pinnacle who are willing to give up their seniority and start over just for the change. I haven’t heard of anyone leaving Mesaba for Pinnacle recently. A year or so ago, Mesaba was a bad place to be, but right now times are good.
On the other hand, upgrade at Pinnacle will likely be faster.