the op stated that he was looking at first gens....so that kinda eliminates 3.0 and 4.0 unless a swap is being done.
so that leaves the 2.0,2.3,2.8,and 2.9.......of this crew i would go 2.9 every time-and if i wanted to upgrade a 4.0 swap would be the next step.
edit-there was one other choice,the 2.3td(ok-two choices....the 2.2 diesel was offered too,stay away)and this would be my #1 choice,if i could find one.