Alright, alright! I agree that Mesa to almost anywhere is a move up. My views may be out of date. In my day, (God that make me feel old) the regionals were strickley turbo props. I'm talking Metros, Bandits, Saab 340, EMB-120s etc. CRJ and ERJ were barely on the drawing board. Todays regionals are a different animal. Still, I would think that a major or large jet operator is the goal for most prospective airline pilots. If that's you, I believe moving from RJ operator to RJ operator just shows a lack of continuity and commitment or, worse yet, terminations.
If you make such a move you need valid reasons to explain to the next interviewer. Valid reasons?
* Other company went out of business
* Spouse transfered across country and you wanted to move there anyway.
* Other company shrinking, losing larger aircraft, upgrade time too long.
* The new company has bigger equipment and is more career oriented.
I've served on interview boards. It's no secret that most pilots are just building time. If I saw a guy coming from a comparable company I would wonder why. If I didn't buy their reasons, I would move on to the next candidate. A shortage of candidates, however, changes things.