If you're going to work for a security agency then G4S is overall the best there is. They offer 401K, healthcare, life insurance, shopping discount benefits through Great 4 Savings, furthering education with accredited colleges at a discount, and more.
Your work environment varies, but you do work very closely with the client at most job sites. You work independently and separately from clients, but your duty is important in that it helps maintaining regular work operations depending on your work site.
Training, professional and friendly supervisors, very organized work sites
Inconvenient Schedules at some work sites