IMHO there no question of this.

Compass if your goal is a mainline job and are only short the jet time vs. all the other criteria mainline wants to see on your resume (college degree, great GPA, rec. letters, etc). The CP just announced 40 new hires and 24 CA upgrades a month indefinitely, in a pilot group of just over 700. Do the math. Assuming this holds true for the next 24 months (AND they can get the recruits), a new hire today would be at the top of the seniority list in less than 2 years and staring an upgrade in the face. Plus CPZ flies the EJET exclusively...meaning that you get a type rating for a jet mainline carriers fly (E170/190 same type)...which makes you THAT much more attractive as a mainline new hire in 4-5 years (ie. they can hire you into their E190 fleet without having the need to pay for new initial type training).

Skywest if you think you could get stuck at a regional in the long-term for any reason. In 44 years of being in business, they have never furloughed a pilot nor gone bankrupt.

IMHO pay and work rules should be last on the list. They are the thing that is changing the fastest for the better and least likely to change for the worse anytime soon.