Let me ask the question a different way:

Have you ever been offroading before (in your own 4x4 vehicle)?

From the way you ask your questions (and the fact that you're asking the question here at all), I doubt it. That's fine... nothing wrong with being a noob...

Is the Rubicon a better rock crawler than the Xterra? Hell yes.

Is the Xterra a good rock crawler and a good/tough offroad vehicle in general? Hell yes.

Since this is your first offroader (I assume) and will be your only vehicle and daily driver (I assume), I think you'll be better served by the Xterra. You won't be disappointed in its offroad capability.

Oh, BTW, you're going to want to modify EITHER vehicle a bit before doing much SERIOUS offroading. Both vehicles need rock sliders (often called rocker knockers in the Heep world) and armor improvements. The Rubicon has this scoop thing that you get stuck on all the time with a factory rig. One thing I can say in favor of the Jeeps - is that they are generally cheaper to upgrade. Since there aren't as many Nissan offroaders, the aftermarket is a bit more expensive.

Anyone else want to post up some offroad pics to show what we can do?







Black Bear Pass in Ouray, CO (not too technically difficult - but very steep and narrow... people slip off it, fall 1000 feet or so, and die from time to time):::

The Steps on Black Bear:






A little poser shot at the bottom of Poughkeepsie Gulch/Engineer Pass trail entrance:


OH - a couple afterthoughts:

The word you were looking for was approach angle. Approach and departure angles determine how steep a climb you can enter/leave without scraping bumper. It's an important thing to think about - but not the end-all-be-all of vehicle comparison criteria.

Water fording: Deep water fording is cool - and you should avoid doing it at all costs. Every vehicle has a depth limit, and whatever that limit is, you'll reach it - and go past it... and quite possibly DESTROY your vehicle by soaking the ECU, sucking water into the engine etc. I'd cross streams up to a couple feet deep without worrying about it too much... but you won't see me doing those water-over-the-hood things that others have posted. It's just too great a risk to the vehicle.