My current #1 is the Conti GP 4000S II.
If I couldn't have these, I'd consider going back to Maxxis Refuse. I had a pair a couple years ago, and went close to 3,000 miles without a flat through gravel, potholes, and random debris. They felt somewhat clunky compared to the 4000S II. Still, not a bad tire, and in my experience, pretty darned reliable.