A combination of hard and soft terrain on the same ride combined with a prayer of longivity generally dictates a soft-to-intermediate tire like the M12 or the Dunlop 756.
The Pirelli MT18s cross over amazingly well as do the Metzler MC4s. Heck, if you throw durability out the window the Michelin S12s work well but will chunk the rear knobs on the hard stuff.
As long as you stay away from a full spike tire on the front you should have good traction. The front generally is a bit more forgiving than the rear, that is the fronts can cross over a broader range of terrain than the rears.
I've got an MT44 front and M12 rear on the KTM 300 right now and it works well in about anything. Granted the MT44 rear almost-paddle tire does better in sand, but it becomes an ice skate on hard pack.
I've got a Dunlop 695 in the back of the XR280 right now and it has surpised the heck out of me. It has done everything from silty dry sand to rocks for hundreds of miles to running it over onto the sidewall on pavement and has performed well.