Pros
The best reason to work for the MTA are that it is a very relaxed environment. They are part government and part private so they do not have pressures that many companies have. The people there thus are relaxed and easy to talk to and friendly. There are not many deadlines, things get done when you get to them. Another important benefit is that once you have a job, it is very hard to lose it. As true for any government job, they are not effected by the business cycle and it does not get effected by wall street. This makes working there more pleasant as you do not have to worry about losing your job.
Cons
The biggest downside of working at the MTA is that they do not pay well. There salaries are very low when you compare them to what you could make in the private sector. What may be worst, is that once you have a job there it is not that easy to move up because people tend to stay there until they retire. This could hamper your progress as you may have to wait years for a promotion when they person above you leaves or takes another position. Also, they pay in a range of what you came in making so if you start off there you will make notably less than someone who came from the outside even if you are doing the same job as them.