Its hard for me to identify a favorite spot. In terms of visual beauty probably new hampshire and maine take the cake. The views out there are just out of this world. Example: https://imgur.com/a/eyAGamT

But in terms of enjoyment each place has its own personality and at each point along the trip you are in a different place physically and mentally, so they are all quite different and unique. For example: the first couple weeks are unbeleivably fun because you cant believe you are actually doing this, even though there wasnt the best weather and not many great views. The middle (PA) is ROCKY and HOT in june/july, but it is dead flat. Virgina goes on foreverrrrrrr. New England is a treat at the end. by that point you are like a machine in terms of hiking. Hell, by Virginia you are a machine. Hard to identify a favorite spot