Not sure why it is but I think you'll find that Mesa is more reliable in terms of on time performance on the West Coast (regardless of what carrier they are operating flights for) than they are on the east (again, regardless of what carrier they are operation for). Also you'll find since you'll be dealing with primarily PHX based inflight crews (every now and then you get a CLT based crew on a west coast flight), that most of the FAs and even the pilots are actually friendly and helpful. The conditions of the aircraft interiors though on Mesa are just down right dumpy. The seats especially on the CRJ900 (which you'll most likely be on) have seat cushions that make you feel like you are sitting on a park bench and the seats are worn. The CRJ200s have slightly more comfortable seat cushions but have leather seats that really just need to be replaced as they are just worn down. I have noticed though a few of their planes that have at least new seat covers.

Your flights won't be the best out there as but I don't think you'll find it that bad.