Here's how I look at it.

Probably, you're not going to go to a major or fractional or wherever you want to go until you've got some substantial PIC time at a 121 operator. Some additional experience as check airman or whatever wouldn't hurt.

Given that that's probably going to take you at least a few years, you should probably spend that time at a company which is going to take reasonably good care of you. In my mind, ExpressJet, Republic, and SkyWest make the short list in no particular order.

I think what it boils down to is how are you going to meet the minimums for one of those companies? You could flight instruct, or you could go to Mesa. To be honest, Mesa might not be a bad way to go, if you know exactly what you're getting in to, expect to be there for as short a time as possible, and expect inhumane, cruel, and abusive treatment. If you're single, money is no object, and you don't mind having 16 hour duty days during which you'll fly 2 hours and maybe get paid for less, it could be for you.

By the way, there's another thread going about how SkyWest lowered their mins to 850tt if you have 200 in a CRJ or equivalent in 121. Mesa to SkyWest wouldn't be a bad plan. You'd be in good company, too.