Four Corners is just a square piece of concrete with the lines drawn on it, a bunch of tourists, and some navajos hawking jewelry - not worth it in my opinion. Monument Valley is easy to drive to, or through as the case may be. It's about 2.5 - 3 hrs from Flagstaff. To go to Four Corners monument adds another hour.
I'm not sure what your itinerary is, but one of my favorite places is Escalante. If you drive down the Hole-in-Rock road there are some GREAT slot canyons - Spooky Gulch, etc. Camping out there is hot, dry, and dusty though. But it's a quick drive up to Aquarius plateau, which is much higher in elevation and cooler. BTW, I highly recommend getting the AAA map called "Indian Country" - it lays out the area on one map so you aren't flipping back and forth from one state to another.
So I used to be a river guide on the Colorado & San Juan river. Have lived on the Colorado side, the New Mexico side, but spent most of my time on the Utah side.
