Any year 96-02 would be good, do some research here to find the model year changes. As for driveability, the Runner will do fine, the 3.4 is a good motor and gets decent mileage for what it is. Driving in the Mts the 3.4 will get the job done, but expect regular downshifts to hold your speed, this is in an auto, never driven a 5 speed 3.4. And unless you want to unlock the T/C or hit 3rd every hill forget about cruise control in the Mts.
While I would never encourage a Nissan over a Toyota, the Pathfinder with the 3.5 V6 would be a decent truck. They definitely have more power than the 3.4 and are built on a unibody so may have a better on pavement ride. Off road a 3rd gen will get you further but the Pathfinder does have a lo range and has decent capability, Personally I don't like the Xterra at all and would never even consider owning one. Plus unless you get a new one you will get the old 3.3 V6, reliability wise it is a good motor, power wise it is a little on the weak side, and remember Nissans are quite a bit heavier than a comparable Toyota.