Pros
Pay, perks, and benefits are great, but the people are amazing. Granted I'm a new hire, but the organization and structure of the company is something I've been searching for, for a long time.
The recruiters are well trained, explaining the duties and responsibilities of the position extremely well. Along with their communication skills being better than any I've experienced thus far.
The support team (HR, IT, logistics, etc) are phenomenal. Utilizing one.mantech.com as your one stop shop to get you everything you need. Pay, benefits explanation, 401k contributions, ordering supplies and equipment, etc. All in one central hub. No filling out x form to submit to y agency, to be put on a waiting list or call back. The support staff is truly exceptional.
Cons
I'm sure something will come up, but so far I'm thoroughly blown away.