Pros
SSAI is a good smaller government contracting company. Although I am employed at this company, I don't know a whole lot about it because I sit at the customer site (NASA), and have very little contact with SSAI. The benefits are good, and the one time I did ask the company for help submitting a grant proposal they were exceptionally helpful. My experience here was somewhat nicer than with SAIC, but since I had little contact with either company, the difference was not significant. Both companies are fine.
Cons
Of course, the only reason a government contracting company exists for science positions is to make it easy for the government to employ soft-money scientists. In that sense I resent this company - it is unethical for someone to profit off of this situation. The story is different for engineering projects, which is the majority of SSAI's business. Other than this vaguely philosophical issue, I have had no negative experiences with the company.