Pros
Working at onsite, you'd get a lot of exposure, that is, if you're really smart and want to improve on your own self. As I see it, placement doesn't happen based on an employee's choice (on 50% of the cases and I can't complain much due to paucity of options for the company and employees). If you prove that you're capable, you're definitely given options to lead/manage teams and they let you do a lot of organizational level activities. You can definitely become a very good sales person and a Manager, if you have some drive.
Cons
1. Salary 2. Even if your immediate boss recognizes you well, the senior management (not all, but a few) think employees are a liability 3. Very Poor in managing appraisals, promotions and compensation 4. Can provide better medical and other benefits, just OK in this regard