Good people, bad management.
While the pay and benefits for ABSc are really nice and at competitive levels, they don't outweigh the negative aspects.
In my experience with ABSC, outside of your immediate site lead, management will always put the wants of the client ahead of their employees. Working your butt off and making your government quota consistently? Well, the government thinks that isn't good enough now and modifies the contract so that the quota is now quadrupled, but with no additional contractor positions. ABSC will sign off on that every time, with no regard to how any change is going to affect their employees.
Also, even after it's widely understood that every employee on the contract has at least an hour long commute home, so they'd rather not drink, at least on person in executive level management will get personally offended if you don't attend their Tuesday, after work happy hour. That type of behavior is unprofessional and extremely petty.
Good benefits and acceptable pay
Poor management, bad company culture, absolute morale killer