What Master's degree is most important for Veterans?

The one you want.

Just like any field, I feel employers do generally look at job experience as a key factor for hiring an individual. Just follow your passion! I just finished my Masters in Public Administration, and I begin class on 31 August for a Ph.D in Public Policy and Homeland Security. My personal interest will be to stay working for the government/ review policy implementations. Far fetched dream, but anything is possible with hard work.

In my opinion for the average Joe (or Jane) coming off of active duty your best bet is to try to build your experience in Project Management. All of us have managed a project in some form or fashion. Get to work on your PMP certification through PMI and work on an MBA that helps you get to that certification if you do not already have it. Now, some may have some specialty that is marketable in the civilian market. My advice is the same, work on the certification and chose a Masters that support that industry.