I think right now, it is tough to rate the Titan against some of the others. Once they get the locking differential, it should be one hell of an off-roader. I remember reading a review in one of the off-road magazines that actually tested a pre-production Titan that actually had the locker and said, something to the effect that the other manufacturers can keep their fancy traction control systems, they prefer the locker. That being said, I would guess that the Titan would be the best off-roader of the full-size trucks.
I admit that I know nothing about the X-Terra. Out of the others you mentioned, I would probably pick the 4-runner for the most versatile off-roader. It has a locking center differential, all the fancy assist gadgets, it has a relatively short wheel base, isn't too wide (like the H2), comes with a v-8 with adequate hp and torque, is based on a truck frame, and is extremely reliable. I was watching a show on the Discovery channel about these researchers that were crossing the arctic. All of their vehicles were 4-Runners with big, wide tires and these really extended guards in the front and rear to prevent them from sinking their tires into crevaces.
Since I don't intend to cross the arctic, the best off-roader for me is the Titan with my KTM in the bed! The truck will get me and the bike as far as I need to go, and the bike will get me over the reeeeeeeeeeeaaaally nasty stuff.