First, just to clear the air... I'm not a MAC pilot, but rather a Line Mechanic with the company. I've been with them for nearly 10 years, now, and have worked at several different stations around the countryside. In general, I like the company, and feel they do the best they can to run a quality operation. I have come to know many of my fellow mechanics personally, and in general feel like we all are sincerely dedicated to keeping the aircraft flying as much as humanly possible, with no compromise to safety.
Now, as to flight crew jobs: I've seen a number of pilots, both left and right seat, come and go. In general, most seem to be reasonably satisfied with their experience with MAC. Of course, there are always those few dissatisfied people, but those are everywhere, right? I could write a book!
Anyway, about the ATR positions. I should think that, if you were to come in with appropriate experience and time as PIC, you could go directly to the left seat of the ATRs. I know it happened several times in the past with the old F27s we've been flying (and still do!), but in each case, it involved an individual with specific and exceptional previous experience.
Pay: well, as I say, I'm a wrench-bender, not a "driver", but F/Os start somewhere around $25k, and Captains (I think) about $42k, with maybe $1k increase each year. Benefits are fairly typical: TCA, health (with dental-good for single man, kinda expensive for family coverage), 401K (vested in 5 years) and a fairly average annual vacation schedule (1 week first year, 2 weeks 2nd year, additional day each year after that.) I will say that, in case of any personal/family emergency, the company seems to go out of their way to be as helpful as they can.
Be aware: you WILL be moving around the countryside! MAC has operations up and down the Eastern seaboard, in the Caribbean, and in South America! You will not, in all probability, be based at any fixed location until you have several years seniority. Keep your bags packed...
All in all, I like MAC. Certainly, there are problems: can you tell me of any company that doesn't have problems? Still, though, the general attitude of the company is one of what I think of as "benevolent professionalism", if that makes any sense. They do seem to try to strike a balance among all the pressures they have to deal with: i.e., the FAA, FedEx, "normal" business pressures, etc., and still deal fairly and honestly with their employees.
Yeah, you might be able to do better, but you could do a LOT worse, too!
See ya!