Pros
STG management listened to their people and really seemed to care about developing employees and making them more than just slot-fillers. The salaries were fair and upper management was very approachable. Lots of opportunity for advancement for motivated and ambitious people. This was the only contractor I've worked for where I truly felt like an employee of a company and not just bound to the government portion of the contract.
Cons
The follow through on paperwork was pretty bad, mistakes were made frequently by upper management. The fact that STG deals with primarily contract work meant that you really were only an employee until another contract was awarded to another company. My time with STG was much shorter than I would have liked. When our contracted was awarded to another company, STG expressed a desire to move some of us to other contracts so that we could remain employees but ultimately it never happened due to the lack of available positions and not enough money on those other contracts.