Whats better a 4x4 or 4x2 Nissan Xterra?

I think you'll find it's more about experience and skill. If you can get some quality off-roading instruction I'd highly recommend it. Then knowing what your vehicle (whatever vehicle) is capable of and not getting in over your head will see you through. And for the times you do get stuck, and you will get stuck no matter how capable your truck or yourself, have a decent winch and know how to use it safely and effectively.