I did a fair amount of backpacking in the past. I've hiked the Loyalsock Trail and the Susquehannock Trial twice each. Now those are great trails in Pennsylvania. As I remeber the Susquehannock is about 85 miles in a circuit. I started in Cross Fork and ended up there. The beer at the hotel was cold! The Loyalsock was about 50 miles long. Some parts were very steep. it seems that the folks who designed it had no idea what a switchback was, since every mountain you climbed the trail went straight up. Did part of the Tuscarora Trail shortly after it was blazed. Not my favorite.
There are parts of the Appalachian trail that I loved hiking back in the 1970s and 1980s. There are also parts I disliked enough never to set foot on them again. The stretch of Pennsylvania from the Delaware Water Gap to the Susquehanna River is one of the latter. It seems that every rock my feet landed on was pointed and hit me right in the middle of a bruise. The section in Clarks Valley through Stony Creek valley is called Saint Anthony's Wilderness, and the trail is not the most user friendly. It is beautiful forest to walk through, though, with some interesting history. At one time the Jesuits had a monestary there and were rumored to have a gold mine which has never been found.
The section from the North Mountain to the South Mountain is almost all roads, and is not much fun IMO. From Churchtown up into the South Mountain and across the Maryland line it is a nice trail to hike. The Potomac Appalachian Trail Club used to have a couple of cabins that you could rent in that stretch, one of which was along Milesburn Road south of Shippensburg. The biggest copperhead I have ever seen was on the stretch just before that cabin.
My W 1 FE unit and I did the stretch from Mount Khatadin through the Presidential mountains of New Hampshire one summer. This is a beautiful section of the trail. At the top of a couple of the big mountains we stayed in what the local trail club called "huts." We got a decent evening meal, a bed to sleep in, and a cooked breakfast for $8.00 each at the time. I did not hike the section from the Presidentials to the Delaware River, so I have no knowledge of that part.
Another part I did hike, this time by myself, was the Shenandoah Park section. This is an interesting hike and the scenery is awesome. The only rattlesnake and the only bear I have seen on the trail were in the park.
I had the ambition at one time in my life to do the entire thing from Springer Mountain in Georgia to Khadadin in Maine, but two things happened. I never had springtime off to start the hike in April, and I got too old (my knees wouldn't take it anymore) so it isn't going to happen. Good luck to anyone who wants to do it.