Having worked for Fairfax they are my favorite of your two choices there. There is more diversity in terms of assignment locations and available job assignments. You can spend a year at GW University to become a paramedic on the helicopter, go into full time or part time tactical team... the list goes on. I think the only thing they didn't have when I was there was a mounted patrol on horses. They have mad money and fantastic equipment as well as top notch training facilities.
The downside is the cost of living but you'll have that problem in Alexandria too...
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The beatings will continue until morale improves.