I have a Pro-106 in Washington County. It works decently about 60% of the time, but simulcast distortion makes it painful to listen to sometimes. The experts can chime in, but I don't know how much this can be blamed on this particular scanner, vs. this problem affecting most scanners trying to monitor this type of system in our geography/topography. As a side note, I can receive Franklin Co., Pa.'s P25 system with a much more consistent strong and clear signal than Wash. Co. Frederick Co., Md not so much, likely due to South Mountain.
Like RDG said above, if you can get a Pro-106 for a really good price, it will do OK for Wash. Co. and several neighboring counties (Franklin in Pa., Berkeley in WV, etc.). But as ka3jjz said, you might consider a scanner that will work with Phase II systems, like the State of Maryland FiRST 700 MHz system, which will be probably be hitting Wash. Co. in the next few years.