The Marble, Middle, and East Forks are all very beautiful. Haven't been up the South Fork yet. There is much to explore off the tourist highways, although those have their own charms here as well!
First visit was in May 2007, I hope to be back next year.
Lived along the banks of the Marble Fork for two summers when I worked at Lodgepole and I have hiked most of the trails in the Kaweah River Canyons.