Pros
Living and working in Washington DC as well as the starting salary, especially for those just out of college. I came to DC for the experience, but not the job. Maybe it is simply learning to adjust to life outside of the protective and fun environment of college, but personal job satisfaction is low. However, your own level of job satisfaction will depend on exactly where you are placed. Some government sites are more exciting and personally fullfulling then others. As a contractor I like the regulations of being held to a 40 hour work week, so I am able to accumulate a great deal of comp time in the process.
Cons
You are contracted out to a government site. There is literally no communication with the company you work for. Your job IS your palcement, not with MPSC. The communication is probably the hardest thing to deal with. Especially when it comes to future salary negotiations, the conversation is a diffilcult one to have since your supervisors know, directly, what your job performace warrants in terms of a raise. Your job palcement supervisor is essentially the one that will agree or not with the company if they want to agree to a raise. Impress those at the work site, not the company itself. As a contracting firm, there is a great deal of disconnect between you and the company.