I believe both are currently hiring pilots. Pinnacle is all CRJs with DTW, MEM, and MSP bases. They will soon have taken delivery of all the jets Northwest currently has slated for them, and that may put the brakes on growth for a while. They do not pay you ANYTHING (no base pay, no per diem, no lodging, nothing) in training until you pass your checkride, which is off-putting for some people. They are also about to get in to contract negotiations which could get ugly, depending on who you talk to.
Mesaba just got a new contract. They are doing some hiring. Flying Saab 340s and Avro RJ85s out of the DTW, MEM, MSP, and CVG bases. They may (or may not) lose the Avros due to their high operating costs, but Northwest has more CRJ options floating out there, and some people think that Mesaba may get those instead of Pinnacle because of the upcoming contract negotiations there.
I don't work for either, but that's what I know. Like John said, N9103M was a Pinnacle pilot, and there is another Pinnacle pilot on the board here ... PeanuckleCRJ I believe. Don't know if we have any Mesaba members or lurkers, though.