Well I can tell you what NOT to get, BFG mud terrains, I had a set a few years ago on a 90 k1500 Chevy and they lasted about 15K and I drove on gravel roads alot back then.
Im loving my Toyo open country A/T's, I have about 8K on them and they are wearing great!
We have also had good luck with Mickey Thompson MTZ on my fathers 01 ram 2500 V10, they have about 15K with about 3/4 tread left, but they spend alot of time on gravel and dirt roads so I'm sure they would be wearing faster it spent more time on asphalt.