I've stayed at 5 of the 7 campgrounds in the immediate Gettysburg area. I like the KOA best as its tucked in the woods at the base of a hill, feels less like a parking lot. Some of the RV sites are on the small side. Granite Hill and Roundtop are both OK and both have wooded and more open areas. Road noise at Roundtop is an issue depending on where your site is. After these three, I'd rate Drummer Boy next and Gettysburg Campground last. Drummer Boy would be great except its literally parallel to a busy highway. Wooded almost throughout and huge, a good mile end-to-end. Gettysburg Campground gets a lot of love but its a flat parking lot, albeit with a large wooded portion. Sites are quite small there IMO.
All of them except the KOA have seasonals, but I saw nothing in the way of junked-up trashy sites at any of them. If quiet evenings matter, the KOA seems to attract the least number of party-hearty folks.
I'll add that we camp twice every October in Gettysburg for Halloween theme weekends. I could go on and on about amenities and activities, but if you just need a base for touring Gettysburg than any of them would be fine.