You have to make up your own mind after researching both Mesaba and Pinnacle. Mesaba has SAABs but also has CRJs (Soon to have more jets on the property). Nothing wrong with SAABs. They will probaly make you a very good stick as you will do lots of takeoffs and landings to many small airports. It would be like getting paid to fly to GA airports that you would enjoy doing anyway (assuming you really like to fly). Upgrade time at Mesaba is now under 1 year. So it is pretty close to what it would be at Pinnacle. Maybe even better. There are FOs with 2 years at Pinnacle who are waiting to upgrade.

QOL by all accounts is probably better at Mesaba. But on the other hand, Pinnacle is also a good airline from what I've heard despite some comments on this forum. They seem like good group of pilots there. So no matter where you decide to go, make the best of it.