I'd start off by saying that an automatic is going to have a lot of the same advantages and disadvantages off road that it has on road.  The auto box is a more complex piece of kit with more potential failure modes, but ultimately very reliable and it provides conveniences.  The manual is more robust and not as much effected by heat, low speed/high load driving, etc, but it's not so convenient to use.

In the type of off roading most people will do the place they'll notice a differnece is on hills.  The torque converter on the auto box gives you a nice de-facto gearing reduction of about 1.5:1 in addition to the gears in the drive line, giving you more power for climbing hills.  On the "down side" (literally) that same effect works in reverse when going down hill, so you don't get as much engine braking effect with the auto box as you do with a manual.  There are of course ways to compensate with the wheel brakes, electronics and things in the transmission or other parts of the drive line, etc.

For the most part I think that any given person's preferences on-road are going to extend to off road.  And that's what we're really talking about here is personal preference.  As Harald aluded to, talking about what some particular kind of competition vehicle uses is of little value to the average joe.  Competition vehicles are designed to meet a very specific set of needs, usually a much narrower set than those of a recreational or part time off road vehicle, so the best solution for one doesn't always trnslate to the best solution for the other.

Whenever someone asks me this kind of question, I usually reply with, "What do you prefer on road?" If you're taking general recreational off road driving as practiced by about the 90th percentile of people using SUVs off road, then they're best off using what they're most comfortable with already.  The particulars of learning to drive well off road will take over and be slightly differnt for each choice, but not horribly significantly so, in my opinion.

-Dave G.

Yep, and I'd agree with them 100%, "...in that situation...." just as I'd probably make the same choice that Kerr's baja truck buildig friends did for their situation.  What I was getting at in my post is that those competitive "situations" can't be taken at face value to represent the recreational user's situation, and that things like robustness and other technical aspects are so close to a wash between the two, that it comes down to a matter of personal preference for all practical purposes.

A related point is probably worth stating too though.  It's without a doubt "easier" to drive an automatic off road without damaging drive line components than it is to drive a manual off road without damaging drive line components (just as it is on road).  Lots of pepole drive manual trans vehicles on road...badly...and tear things up.  Not particularly related to whether one mechanical component is "better" suited to the purpose of moving the vehicle around, but more to whether or not the individual cares to become proficient with the tool. 

It's along these lines that the "tread lightly" guy in me says, get the auto box because more people can use it mindlessly without tearing up the terrain, even though the well-used manual can be argued to ultimately be easier on the ground.  Again, not related to whether one is better suited to the task, but rather which is less likely to be minsused in the hands of a casual user.

Fun stuff!

-Dave G.