I live right across the river from Lancaster. We have stayed at Old Mill Stream CG with friends. It is right beside Dutch Wonderland, so if you have young kids... Even w/o kids it is a very nice CG, and it's far enough back off the road, that I didn't notice traffic noise when we were there. There are a lot of Outlets in that area.
Gettysburg will probably be an hour or hour and a half from Lancaster.
I'd stay at one area, see what you want to see, and then move to a CG in the other area.
Gettysburg has a lot of historical things to see. I much prefer G'burg over Lancaster. Lancaster has a lot of Amish attractions. There is Dutch Wonderland -- Hershey Park is nearby. Strasburg Railroad is good to see. Shady Maple Smorgasbord is supposed to be a fabulous place to eat.
York has the Harley Davidson Museum, and they do factory tours. There is an Industrial Museum in York.