I would hesitate to call any tour the best because the experience can vary so much depending on the weather, time, distance, scenery, etc.
The bike tour that I have enjoyed the most is the New River Trail in SW Virginia. It is extremely scenic, lightly traveled with no car traffic, mostly flat and has nice campgrounds. However, the trail is only about 60 miles long, so it's a 1-2 day tour at best. The C&O Canal - GAP trail offers a similar experience and could be ridden in 3-7 days, depending on how far you want to ride each day. Both of these trails are more suitable for cross bikes, mountain bikes or touring bikes with fatter tires. They are ideal during favorable weather conditions but could be miserable during cold, extremely hot or rainy weather, and storms could block passage if winds are strong enough to topple trees and limbs -- which happens on occasion.
Another tour that I enjoyed tremendously was riding in the "driftless zone" of SW Wisconsin. We were based out of Sparta, WI, for the entire week, with loop rides starting and ending in town each day. I really enjoyed that tour because the scenery was quite different each day, depending on the direction we went. We also rode one day on the Sparta-Elroy trail, which is supposedly the original "rails to trails" project.