Tarptents are a terrific choice on the A.T. They are light, airy, bug proof, and very protective in a rain storm. When we take 2 or 3 people on an AT hike, our Rainshadow is the perfect shelter.
For me as a solo hiker, I go with the small tarp/bivy combo for the versatility, as mentioned above. However, if I were planning a thru-hike, I would take a hard look at one of the solo Tarptents.