Since the cars you are planning buy are of a rather old model, do expect to spend some money on its maintenance. This applies to both the types you are planning to buy.
Go for the Xterra. We have some of the cheapest petrol/gas in the world so I wouldn't be too concerned about fuel economy - but don't forget the environment.
Pathfinder will be cheaper for repairs. Both are good. If you get any one in good condition, go for it. Also consider the Pajero.
I would suggest pathfinder since most mechanics can work on them since they are more common. The fuel consumption is going to be the same since both of them have the same engine.