for offroading automatic put less stress on other parts like axles driveshafts and suspension components. Also, clutches don't any way of staying cool. automatic transmissions have coolers and bigger cooler can be added. 6 cyl ford explorers have bad transmissions, I would get a manual there.
Automatics have a much smoother application of torque than manuals. Automatic multiply torque in the converter. Don't worry about being underpowered, your only going 5 mph. If you have a underpowered vehicle, don't put oversized tires on them without regearing. If serious enthusiast offroading is done 33's do fine on jeeps, suv's and trucks.
I've seen some very competent 4 cylinder jeeps out on the trails. The best mildly modified offroad machine hands down are suzuki samari's. With some 31's and a cheap offroad kit, they haul.
For survivalist reasons. Any 4 wheel drive with a decent amount of ground clearance and cargo will do. Just make sure it has factory skid plates, 31 inch tires, and good points where you can hook up recovery chains. Make sure you have a truck based 4 wheeler with a 4lo range. Those honda, toyota, and other cars on steroids are useless. though some truck based toyotas are decent. A rear locker, trans cooler, and winch is a nice addition in that order. Get a full sized spare and have a offroad jack like a hi-lift. also, doubles as a winch too (with cable).
http://www.hi-lift.com/hi-lift-jacks/all-cast.html Anything else is more for fun. Which is fine with me. Where you need to go and stay put. Just chop a tree down on the trail, that keep you secluded. Humvee's suck as far as offroading. They weigh too much for their tires. Their long wheel base makes their lift not as good as you think. And, very few woodlands trails are wide enough for humvee's. So don't worry about hiding from miltary vehicles as much. Seen these things in action in the mortheast, they as good as a mild modded jeep.
A quick way to kill any drivetrain. Using chains to yank stuff out with. Chains don't have a give and put a nice whap on gear teeth and stamped metal transmission parts. Get a nylon strap, then you can hook cable or chain to it. 10 ft min. Also, huge crane straps don't have enough give. The spring in the nylon can also help you get out with one tug. A good amount of times offroading before I got a winch, I took a comealong and snug up a 30ft nylon to the point where it just starts to push the car out. Get back in and go. That strap gives you about a half foot of push, enough to get some momentum.