I just completed a tour from NH to DC. I picked up the PA section of the ACA route at French Creek State Park. Their route on through the PA Dutch country was excellent. After the Susquehanna bridge at Columbia consider leaving the ACA route at PA 624 not far past Wrightsville on ACA map 29. Following secondary roads on the PA road map will lead you in a more westerly direction through Red Lion, Glen Rock and on into MD at Lineboro. From there follow MD secondary roads to Westminster.

From Westminster it is a straight shot down route 27 to Germantown. A little more traffic than desirable but it is a designated bike route with a wide safe shoulder for the most part, occasional bike lane markings and pleasant rural scenery. Alternatively you could take MD 75 and 109 further west for less traffic.

From Germantown I used Google bike maps to connect me to the C&O canal but it dead ended me on a bike path in Gaithersburg on a pond in a residential area. I reverted to paper maps and followed Darnestown Rd to Travilah Rd to Piney Meetinghouse Rd which took me right to Swain's Lock on the C&O where there is a hiker/biker camp. From there it's an easy 15 mile cruise into DC. 700x32 Gatorskins worked fine.

I've never taken the ACA route through MD but it seems to be and endless succession of twist and turns just to route the rider through Baltimore and DC suburbs and finally into DC on the wrong side.