Pros
If you are on contract the best is the opportunity to work at a client site, where you may be appreciated enough to be seen and hired as a direct employee.
Cons
The quality of your work environment under contract will clearly be highly dependent on your immediate supervisor. They obviously will make the difference between good culture, motivated employees, and team morale. You should interview them as strongly as they interview you. Remember to separate out their desires and intents from the things they can actually control, which will be very few. I cannot recommend them for compensation, growth, benefits, or other services provided by the corporate offices. View your immediate manager as attempting to serve multiple masters, since the client will be at the top of the list, followed by the corporate office and policy, followed by your manager's intent and skills.