It really will be driven by what you decide you want/need your degree to be in. That said, UMUC has a wide variety of Master's degrees, as well as an established path for dual Masters of whatever/MBA.
If you JUST want the degree, and don't care what, as a History type, looking into Norwich's Masters in Mil History might be a lot of fun.
You can not go wrong with a Masters in Project Management or a Masters in Business Administration (Insert focus here). The MBA lists a number of different concentrations to tailor to what you may want to do in post Army life. Another good thing about most MBAs is that the original course line is exactly the same and you don't have to decide until after the 6 basic courses on where you should direct your concentration. Like a lot of those who have commented below, I too am a student of Columbia Southern University. I completed my Bachelors with them and have opted to stick with them for my Masters. Very easy to work with, option for extensions if work ends up interfering with completion date, and a dedicated staff to ensure your success.
Whatever you chose, good luck. I have noticed a drastically different course load across the handful of classes I have taken on the graduate level.