MSP is a Skywest base and you're already holding it? Is it also a Jr captain base? If Delta/United are your ultimate goal, then stick with the job that will get you an upgrade the quickest. If you've currently got good quality of life, then why change anything? If you'd have to commute to sit reserve once you upgrade at Skywest, I'd consider the Sun Country move...but as others have said, you gotta interview first. There's no decision to make until you have an offer.