Hard choice, they're all beautiful! In addition to the resources Chris mentioned, I find the "Guide to Arizona Backroads & 4-Wheel Drive Trails", by Charles A. Wells to be very helpful. There are several fun trails in the Sedona area, and some dispersed camping not too far from town. And, of course, Flagstaff is very close to Coconino National Forest, with lots of opportunities there. As for the Grand Canyon, they don't call it "Grand" for nothing!
A few years ago, Robin and I very much enjoyed a trip south on the Senator Highway from Prescott almost all the way down to Lake Pleasant, and then west to Wickenburg. It was off-road almost the entire way. We went from higher elevation pine forest down to the desert and through a Saguaro cactus forest. There was lots of opportunity for dispersed camping. Of the four possibilities that you've mentioned, that may be the most similar to the Mojave or Saline Valley Roads.
The area from Fredonia south to the North Rim of the Grand Canyon may also offer some similar mild off-road and dispersed camping opportunities in the Kaibab National Forest. I'm very jealous, but I hope you have a great time!
