Pros
It used to be the benefits. However, since we have fallen under the Service Contract Act (SCA), that is no longer the case. Because of the SCA, if you are just starting on with ManTech or another contractor, then your benefits are not as good as they were prior. If you are starting out now, you will never ever have any sick time, which is rediculous.
Cons
It is a white, male dominated company. If you are not a white male who is part of a very small clique you will never get anywhere, no matter how educated or qualified you are. I know this through my own experience as well as people I work with. I finally got promoted into a position which was created for a white male and was filled by another male that I trained, and found out through the grapevine that I was making much less than either of them had started at.