hoover

What's the overall goal of the OP? If it's to go to a major don't worry about type just go with who gets you to left seat the quickest then who can offer instructor /check airman advancement. Going to an ACMI outfit with 737 will ensure that you be flying 737 but that's about it. Slow time building, few advancement opportunities, lower pay, less bennies but the crews you work with will be the most rememberable you'll ever work with.
Just based on flying the 737 and nothing else I'd go to sun country. Either they'll continue to plug away and be in business for a while or get bought by someone . I'd consider them a step up from swift or southern

saab2000

Can't speak about the others, but Sun Country is a real airline with real schedules. I spent a year there and there are way worse places to be based on what I've heard.

That said, it's not a place to think you'll just skate through training. It's a tough training program with high expectations.

But there are two things to note: Pay isn't great by a long shot. It was a huge pay cut for me coming from the left seat of a CRJ. Be ready for that. Also, move to MSP if you go there and aren't from there. It's not a commuter-friendly place. That's not intentional but it's not their business model. Living in domicile and working for SY isn't a bad gig but I can't really imagine commuting there as you'll be on RSV doing a lot of day trips and some multi-day trips.

I'd be more inclined to go to one of the more established regionals though and looking at one with a flow to their major and good movement on the seniority list.

Of the ones listed, SY is the only place to consider a "Career" because QOL can be pretty decent living in MSP. The other places tend to be places you end up at and can't ever leave. SY is generally respected throughout the industry.